| Message ID | 20221117221758.66326-2-scgl@linux.ibm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg | expand |
On Thu, 17 Nov 2022 23:17:50 +0100 Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote: > User space can use the MEM_OP ioctl to make storage key checked reads > and writes to the guest, however, it has no way of performing atomic, > key checked, accesses to the guest. > Extend the MEM_OP ioctl in order to allow for this, by adding a cmpxchg > mode. For now, support this mode for absolute accesses only. > > This mode can be use, for example, to set the device-state-change > indicator and the adapter-local-summary indicator atomically. > > Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> > --- > include/uapi/linux/kvm.h | 5 ++ > arch/s390/kvm/gaccess.h | 3 ++ > arch/s390/kvm/gaccess.c | 101 +++++++++++++++++++++++++++++++++++++++ > arch/s390/kvm/kvm-s390.c | 35 +++++++++++++- > 4 files changed, 142 insertions(+), 2 deletions(-) > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 0d5d4419139a..1f36be5493e6 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -588,6 +588,8 @@ struct kvm_s390_mem_op { > struct { > __u8 ar; /* the access register number */ > __u8 key; /* access key, ignored if flag unset */ > + __u8 pad1[6]; /* ignored */ > + __u64 old_p; /* ignored if flag unset */ > }; > __u32 sida_offset; /* offset into the sida */ > __u8 reserved[32]; /* ignored */ > @@ -604,6 +606,9 @@ struct kvm_s390_mem_op { > #define KVM_S390_MEMOP_F_CHECK_ONLY (1ULL << 0) > #define KVM_S390_MEMOP_F_INJECT_EXCEPTION (1ULL << 1) > #define KVM_S390_MEMOP_F_SKEY_PROTECTION (1ULL << 2) > +#define KVM_S390_MEMOP_F_CMPXCHG (1ULL << 3) > +/* Non program exception return codes (pgm codes are 16 bit) */ > +#define KVM_S390_MEMOP_R_NO_XCHG ((1 << 16) + 0) are you planning to have further *_R_* macros in the near future? if not, remove the + 0 if yes, move the (1 << 16) to a macro, so it becomes something like (KVM_S390_MEMOP_R_BASE + 0) (maybe you can find a better/shorter name) > > /* for KVM_INTERRUPT */ > struct kvm_interrupt { > diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h > index 9408d6cc8e2c..92a3b9fb31ec 100644 > --- a/arch/s390/kvm/gaccess.h > +++ b/arch/s390/kvm/gaccess.h > @@ -206,6 +206,9 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, > int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra, > void *data, unsigned long len, enum gacc_mode mode); > > +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, > + __uint128_t *old, __uint128_t new, u8 access_key); > + > /** > * write_guest_with_key - copy data from kernel space to guest space > * @vcpu: virtual cpu > diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c > index 0243b6e38d36..be042865d8a1 100644 > --- a/arch/s390/kvm/gaccess.c > +++ b/arch/s390/kvm/gaccess.c > @@ -1161,6 +1161,107 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra, > return rc; > } > > +/** > + * cmpxchg_guest_abs_with_key() - Perform cmpxchg on guest absolute address. > + * @kvm: Virtual machine instance. > + * @gpa: Absolute guest address of the location to be changed. > + * @len: Operand length of the cmpxchg, required: 1 <= len <= 16. Providing a > + * non power of two will result in failure. > + * @old_p: Pointer to old value. If the location at @gpa contains this value, the > + * exchange will succeed. After calling cmpxchg_guest_abs_with_key() *@old > + * contains the value at @gpa before the attempt to exchange the value. > + * @new: The value to place at @gpa. > + * @access_key: The access key to use for the guest access. > + * > + * Atomically exchange the value at @gpa by @new, if it contains *@old. > + * Honors storage keys. > + * > + * Return: * 0: successful exchange > + * * 1: exchange unsuccessful > + * * a program interruption code indicating the reason cmpxchg could > + * not be attempted > + * * -EINVAL: address misaligned or len not power of two > + * * -EAGAIN: transient failure (len 1 or 2) please also document -EOPNOTSUPP > + */ > +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, > + __uint128_t *old_p, __uint128_t new, > + u8 access_key) > +{ > + gfn_t gfn = gpa >> PAGE_SHIFT; > + struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); exchange the above two lines (reverse christmas tree) > + bool writable; > + hva_t hva; > + int ret; > + > + if (!IS_ALIGNED(gpa, len)) > + return -EINVAL; > + > + hva = gfn_to_hva_memslot_prot(slot, gfn, &writable); > + if (kvm_is_error_hva(hva)) > + return PGM_ADDRESSING; > + /* > + * Check if it's a read-only memslot, even though that cannot occur > + * since those are unsupported. > + * Don't try to actually handle that case. > + */ > + if (!writable) > + return -EOPNOTSUPP; either you document this, or you return something else (like -EINVAL) > + > + hva += offset_in_page(gpa); > + switch (len) { > + case 1: { > + u8 old; > + > + ret = cmpxchg_user_key((u8 *)hva, &old, *old_p, new, access_key); > + ret = ret < 0 ? ret : old != *old_p; > + *old_p = old; > + break; > + } > + case 2: { > + u16 old; > + > + ret = cmpxchg_user_key((u16 *)hva, &old, *old_p, new, access_key); > + ret = ret < 0 ? ret : old != *old_p; > + *old_p = old; > + break; > + } > + case 4: { > + u32 old; > + > + ret = cmpxchg_user_key((u32 *)hva, &old, *old_p, new, access_key); > + ret = ret < 0 ? ret : old != *old_p; > + *old_p = old; > + break; > + } > + case 8: { > + u64 old; > + > + ret = cmpxchg_user_key((u64 *)hva, &old, *old_p, new, access_key); > + ret = ret < 0 ? ret : old != *old_p; > + *old_p = old; > + break; > + } > + case 16: { > + __uint128_t old; > + > + ret = cmpxchg_user_key((__uint128_t *)hva, &old, *old_p, new, access_key); > + ret = ret < 0 ? ret : old != *old_p; > + *old_p = old; > + break; I really dislike repeating the same code 5 times, but I guess there was no other way? > + } > + default: > + return -EINVAL; > + } > + mark_page_dirty_in_slot(kvm, slot, gfn); > + /* > + * Assume that the fault is caused by protection, either key protection > + * or user page write protection. > + */ > + if (ret == -EFAULT) > + ret = PGM_PROTECTION; > + return ret; > +} > + > /** > * guest_translate_address_with_key - translate guest logical into guest absolute address > * @vcpu: virtual cpu > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 45d4b8182b07..2410b4044283 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -576,7 +576,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > case KVM_CAP_S390_VCPU_RESETS: > case KVM_CAP_SET_GUEST_DEBUG: > case KVM_CAP_S390_DIAG318: > - case KVM_CAP_S390_MEM_OP_EXTENSION: > r = 1; > break; > case KVM_CAP_SET_GUEST_DEBUG2: > @@ -590,6 +589,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > case KVM_CAP_S390_MEM_OP: > r = MEM_OP_MAX_SIZE; > break; > + case KVM_CAP_S390_MEM_OP_EXTENSION: > + /* > + * Flag bits indicating which extensions are supported. > + * The first extension doesn't use a flag, but pretend it does, > + * this way that can be changed in the future. > + */ > + r = 0x3; > + break; > case KVM_CAP_NR_VCPUS: > case KVM_CAP_MAX_VCPUS: > case KVM_CAP_MAX_VCPU_ID: > @@ -2714,12 +2721,19 @@ static bool access_key_invalid(u8 access_key) > static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) > { > void __user *uaddr = (void __user *)mop->buf; > + void __user *old_p = (void __user *)mop->old_p; > + union { > + __uint128_t quad; > + char raw[sizeof(__uint128_t)]; > + } old = { .quad = 0}, new = { .quad = 0 }; > + unsigned int off_in_quad = sizeof(__uint128_t) - mop->size; > u64 supported_flags; > void *tmpbuf = NULL; > int r, srcu_idx; > > supported_flags = KVM_S390_MEMOP_F_SKEY_PROTECTION > - | KVM_S390_MEMOP_F_CHECK_ONLY; > + | KVM_S390_MEMOP_F_CHECK_ONLY > + | KVM_S390_MEMOP_F_CMPXCHG; > if (mop->flags & ~supported_flags || !mop->size) > return -EINVAL; > if (mop->size > MEM_OP_MAX_SIZE) > @@ -2741,6 +2755,15 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) > } else { > mop->key = 0; > } > + if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) { add a quick comment here to explain that this check validates off_in_quad, and that it does not do a full validation of mop->size, which will happen in cmpxchg_guest_abs_with_key. > + if (mop->size > sizeof(new)) > + return -EINVAL; > + /* off_in_quad has been validated */ > + if (copy_from_user(&new.raw[off_in_quad], uaddr, mop->size)) > + return -EFAULT; > + if (copy_from_user(&old.raw[off_in_quad], old_p, mop->size)) > + return -EFAULT; > + } > if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) { > tmpbuf = vmalloc(mop->size); > if (!tmpbuf) > @@ -2771,6 +2794,14 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) > case KVM_S390_MEMOP_ABSOLUTE_WRITE: { > if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) { > r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_STORE, mop->key); > + } else if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) { > + r = cmpxchg_guest_abs_with_key(kvm, mop->gaddr, mop->size, > + &old.quad, new.quad, mop->key); > + if (r == 1) { > + r = KVM_S390_MEMOP_R_NO_XCHG; I wonder if you could not simplify things by returning directly KVM_S390_MEMOP_R_NO_XCHG instead of 1 > + if (copy_to_user(old_p, &old.raw[off_in_quad], mop->size)) > + r = -EFAULT; > + } > } else { > if (copy_from_user(tmpbuf, uaddr, mop->size)) { > r = -EFAULT;
On Thu, 2022-12-01 at 17:15 +0100, Claudio Imbrenda wrote: > On Thu, 17 Nov 2022 23:17:50 +0100 > Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote: > > > User space can use the MEM_OP ioctl to make storage key checked reads > > and writes to the guest, however, it has no way of performing atomic, > > key checked, accesses to the guest. > > Extend the MEM_OP ioctl in order to allow for this, by adding a cmpxchg > > mode. For now, support this mode for absolute accesses only. > > > > This mode can be use, for example, to set the device-state-change > > indicator and the adapter-local-summary indicator atomically. > > > > Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> > > --- > > include/uapi/linux/kvm.h | 5 ++ > > arch/s390/kvm/gaccess.h | 3 ++ > > arch/s390/kvm/gaccess.c | 101 +++++++++++++++++++++++++++++++++++++++ > > arch/s390/kvm/kvm-s390.c | 35 +++++++++++++- > > 4 files changed, 142 insertions(+), 2 deletions(-) > > > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > > index 0d5d4419139a..1f36be5493e6 100644 > > --- a/include/uapi/linux/kvm.h > > +++ b/include/uapi/linux/kvm.h > > @@ -588,6 +588,8 @@ struct kvm_s390_mem_op { > > struct { > > __u8 ar; /* the access register number */ > > __u8 key; /* access key, ignored if flag unset */ > > + __u8 pad1[6]; /* ignored */ > > + __u64 old_p; /* ignored if flag unset */ > > }; > > __u32 sida_offset; /* offset into the sida */ > > __u8 reserved[32]; /* ignored */ > > @@ -604,6 +606,9 @@ struct kvm_s390_mem_op { > > #define KVM_S390_MEMOP_F_CHECK_ONLY (1ULL << 0) > > #define KVM_S390_MEMOP_F_INJECT_EXCEPTION (1ULL << 1) > > #define KVM_S390_MEMOP_F_SKEY_PROTECTION (1ULL << 2) > > +#define KVM_S390_MEMOP_F_CMPXCHG (1ULL << 3) > > +/* Non program exception return codes (pgm codes are 16 bit) */ > > +#define KVM_S390_MEMOP_R_NO_XCHG ((1 << 16) + 0) > > are you planning to have further *_R_* macros in the near future? > if not, remove the + 0 No, we can indeed just add it back if there ever are additional ones. > if yes, move the (1 << 16) to a macro, so it becomes something like > (KVM_S390_MEMOP_R_BASE + 0) > > (maybe you can find a better/shorter name) > > > > > /* for KVM_INTERRUPT */ > > struct kvm_interrupt { > > diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h > > index 9408d6cc8e2c..92a3b9fb31ec 100644 > > --- a/arch/s390/kvm/gaccess.h > > +++ b/arch/s390/kvm/gaccess.h > > @@ -206,6 +206,9 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, > > int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra, > > void *data, unsigned long len, enum gacc_mode mode); > > > > +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, > > + __uint128_t *old, __uint128_t new, u8 access_key); > > + > > /** > > * write_guest_with_key - copy data from kernel space to guest space > > * @vcpu: virtual cpu > > diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c > > index 0243b6e38d36..be042865d8a1 100644 > > --- a/arch/s390/kvm/gaccess.c > > +++ b/arch/s390/kvm/gaccess.c > > @@ -1161,6 +1161,107 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra, > > return rc; > > } > > > > +/** > > + * cmpxchg_guest_abs_with_key() - Perform cmpxchg on guest absolute address. > > + * @kvm: Virtual machine instance. > > + * @gpa: Absolute guest address of the location to be changed. > > + * @len: Operand length of the cmpxchg, required: 1 <= len <= 16. Providing a > > + * non power of two will result in failure. > > + * @old_p: Pointer to old value. If the location at @gpa contains this value, the > > + * exchange will succeed. After calling cmpxchg_guest_abs_with_key() *@old > > + * contains the value at @gpa before the attempt to exchange the value. > > + * @new: The value to place at @gpa. > > + * @access_key: The access key to use for the guest access. > > + * > > + * Atomically exchange the value at @gpa by @new, if it contains *@old. > > + * Honors storage keys. > > + * > > + * Return: * 0: successful exchange > > + * * 1: exchange unsuccessful > > + * * a program interruption code indicating the reason cmpxchg could > > + * not be attempted > > + * * -EINVAL: address misaligned or len not power of two > > + * * -EAGAIN: transient failure (len 1 or 2) > > please also document -EOPNOTSUPP I'd add "* -EOPNOTSUPP: should never occur", then, that ok with you? > > > + */ > > +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, > > + __uint128_t *old_p, __uint128_t new, > > + u8 access_key) > > +{ > > + gfn_t gfn = gpa >> PAGE_SHIFT; > > + struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); > > exchange the above two lines (reverse christmas tree) Is this a hard requirement? Since there is a dependency. If I do the initialization further down, the order wouldn't actually change. > > > + bool writable; > > + hva_t hva; > > + int ret; > > + > > + if (!IS_ALIGNED(gpa, len)) > > + return -EINVAL; > > + > > + hva = gfn_to_hva_memslot_prot(slot, gfn, &writable); > > + if (kvm_is_error_hva(hva)) > > + return PGM_ADDRESSING; > > + /* > > + * Check if it's a read-only memslot, even though that cannot occur > > + * since those are unsupported. > > + * Don't try to actually handle that case. > > + */ > > + if (!writable) > > + return -EOPNOTSUPP; > > either you document this, or you return something else (like -EINVAL) > > > + > > + hva += offset_in_page(gpa); > > + switch (len) { > > + case 1: { > > + u8 old; > > + > > + ret = cmpxchg_user_key((u8 *)hva, &old, *old_p, new, access_key); > > + ret = ret < 0 ? ret : old != *old_p; > > + *old_p = old; > > + break; > > + } > > + case 2: { > > + u16 old; > > + > > + ret = cmpxchg_user_key((u16 *)hva, &old, *old_p, new, access_key); > > + ret = ret < 0 ? ret : old != *old_p; > > + *old_p = old; > > + break; > > + } > > + case 4: { > > + u32 old; > > + > > + ret = cmpxchg_user_key((u32 *)hva, &old, *old_p, new, access_key); > > + ret = ret < 0 ? ret : old != *old_p; > > + *old_p = old; > > + break; > > + } > > + case 8: { > > + u64 old; > > + > > + ret = cmpxchg_user_key((u64 *)hva, &old, *old_p, new, access_key); > > + ret = ret < 0 ? ret : old != *old_p; > > + *old_p = old; > > + break; > > + } > > + case 16: { > > + __uint128_t old; > > + > > + ret = cmpxchg_user_key((__uint128_t *)hva, &old, *old_p, new, access_key); > > + ret = ret < 0 ? ret : old != *old_p; > > + *old_p = old; > > + break; > > I really dislike repeating the same code 5 times, but I guess there was > no other way? I could use the function called by cmpxchg_user_key directly, but Heiko won't agree to that. A macro would work too, of course, not sure if I prefer that tho. > > > + } > > + default: > > + return -EINVAL; > > + } > > + mark_page_dirty_in_slot(kvm, slot, gfn); > > + /* > > + * Assume that the fault is caused by protection, either key protection > > + * or user page write protection. > > + */ > > + if (ret == -EFAULT) > > + ret = PGM_PROTECTION; > > + return ret; > > +} > > + > > /** > > * guest_translate_address_with_key - translate guest logical into guest absolute address > > * @vcpu: virtual cpu > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > > index 45d4b8182b07..2410b4044283 100644 > > --- a/arch/s390/kvm/kvm-s390.c > > +++ b/arch/s390/kvm/kvm-s390.c > > @@ -576,7 +576,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > > case KVM_CAP_S390_VCPU_RESETS: > > case KVM_CAP_SET_GUEST_DEBUG: > > case KVM_CAP_S390_DIAG318: > > - case KVM_CAP_S390_MEM_OP_EXTENSION: > > r = 1; > > break; > > case KVM_CAP_SET_GUEST_DEBUG2: > > @@ -590,6 +589,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > > case KVM_CAP_S390_MEM_OP: > > r = MEM_OP_MAX_SIZE; > > break; > > + case KVM_CAP_S390_MEM_OP_EXTENSION: > > + /* > > + * Flag bits indicating which extensions are supported. > > + * The first extension doesn't use a flag, but pretend it does, > > + * this way that can be changed in the future. > > + */ > > + r = 0x3; > > + break; > > case KVM_CAP_NR_VCPUS: > > case KVM_CAP_MAX_VCPUS: > > case KVM_CAP_MAX_VCPU_ID: > > @@ -2714,12 +2721,19 @@ static bool access_key_invalid(u8 access_key) > > static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) > > { > > void __user *uaddr = (void __user *)mop->buf; > > + void __user *old_p = (void __user *)mop->old_p; > > + union { > > + __uint128_t quad; > > + char raw[sizeof(__uint128_t)]; > > + } old = { .quad = 0}, new = { .quad = 0 }; > > + unsigned int off_in_quad = sizeof(__uint128_t) - mop->size; > > u64 supported_flags; > > void *tmpbuf = NULL; > > int r, srcu_idx; > > > > supported_flags = KVM_S390_MEMOP_F_SKEY_PROTECTION > > - | KVM_S390_MEMOP_F_CHECK_ONLY; > > + | KVM_S390_MEMOP_F_CHECK_ONLY > > + | KVM_S390_MEMOP_F_CMPXCHG; > > if (mop->flags & ~supported_flags || !mop->size) > > return -EINVAL; > > if (mop->size > MEM_OP_MAX_SIZE) > > @@ -2741,6 +2755,15 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) > > } else { > > mop->key = 0; > > } > > + if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) { > > add a quick comment here to explain that this check validates > off_in_quad, and that it does not do a full validation of mop->size, > which will happen in cmpxchg_guest_abs_with_key. Will do. > > > + if (mop->size > sizeof(new)) > > + return -EINVAL; > > + /* off_in_quad has been validated */ > > + if (copy_from_user(&new.raw[off_in_quad], uaddr, mop->size)) > > + return -EFAULT; > > + if (copy_from_user(&old.raw[off_in_quad], old_p, mop->size)) > > + return -EFAULT; > > + } > > if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) { > > tmpbuf = vmalloc(mop->size); > > if (!tmpbuf) > > @@ -2771,6 +2794,14 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) > > case KVM_S390_MEMOP_ABSOLUTE_WRITE: { > > if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) { > > r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_STORE, mop->key); > > + } else if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) { > > + r = cmpxchg_guest_abs_with_key(kvm, mop->gaddr, mop->size, > > + &old.quad, new.quad, mop->key); > > + if (r == 1) { > > + r = KVM_S390_MEMOP_R_NO_XCHG; > > I wonder if you could not simplify things by returning directly > KVM_S390_MEMOP_R_NO_XCHG instead of 1 To me it feels like KVM_S390_MEMOP_R_NO_XCHG is api surface and should be referenced here. cmpxchg_guest_abs_with_key isn't mem op specific (of course that's the only thing it is currently used for). > > > + if (copy_to_user(old_p, &old.raw[off_in_quad], mop->size)) > > + r = -EFAULT; > > + } > > } else { > > if (copy_from_user(tmpbuf, uaddr, mop->size)) { > > r = -EFAULT; >
On Thu, 01 Dec 2022 18:44:56 +0100 Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote: > > > > please also document -EOPNOTSUPP > > I'd add "* -EOPNOTSUPP: should never occur", then, that ok with you? no, also explain in which conditions it is returned something like: * -EOPNOTSUPP: if the memslot is not writable (should never occour) > > > > > + */ > > > +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, > > > + __uint128_t *old_p, __uint128_t new, > > > + u8 access_key) > > > +{ > > > + gfn_t gfn = gpa >> PAGE_SHIFT; > > > + struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); > > > > exchange the above two lines (reverse christmas tree) > > Is this a hard requirement? Since there is a dependency. > If I do the initialization further down, the order wouldn't actually change. ahhhhh right, I had missed that keep it as it is, of course [...] > > I really dislike repeating the same code 5 times, but I guess there was > > no other way? > > I could use the function called by cmpxchg_user_key directly, but Heiko won't agree to that. > A macro would work too, of course, not sure if I prefer that tho. ok so there is no other way, let's keep it as it is [...] > To me it feels like KVM_S390_MEMOP_R_NO_XCHG is api surface and should be referenced here. > cmpxchg_guest_abs_with_key isn't mem op specific > (of course that's the only thing it is currently used for). fair enough > > > > > + if (copy_to_user(old_p, &old.raw[off_in_quad], mop->size)) > > > + r = -EFAULT; > > > + } > > > } else { > > > if (copy_from_user(tmpbuf, uaddr, mop->size)) { > > > r = -EFAULT; > > >
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 0d5d4419139a..1f36be5493e6 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -588,6 +588,8 @@ struct kvm_s390_mem_op { struct { __u8 ar; /* the access register number */ __u8 key; /* access key, ignored if flag unset */ + __u8 pad1[6]; /* ignored */ + __u64 old_p; /* ignored if flag unset */ }; __u32 sida_offset; /* offset into the sida */ __u8 reserved[32]; /* ignored */ @@ -604,6 +606,9 @@ struct kvm_s390_mem_op { #define KVM_S390_MEMOP_F_CHECK_ONLY (1ULL << 0) #define KVM_S390_MEMOP_F_INJECT_EXCEPTION (1ULL << 1) #define KVM_S390_MEMOP_F_SKEY_PROTECTION (1ULL << 2) +#define KVM_S390_MEMOP_F_CMPXCHG (1ULL << 3) +/* Non program exception return codes (pgm codes are 16 bit) */ +#define KVM_S390_MEMOP_R_NO_XCHG ((1 << 16) + 0) /* for KVM_INTERRUPT */ struct kvm_interrupt { diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h index 9408d6cc8e2c..92a3b9fb31ec 100644 --- a/arch/s390/kvm/gaccess.h +++ b/arch/s390/kvm/gaccess.h @@ -206,6 +206,9 @@ int access_guest_with_key(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra, void *data, unsigned long len, enum gacc_mode mode); +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, + __uint128_t *old, __uint128_t new, u8 access_key); + /** * write_guest_with_key - copy data from kernel space to guest space * @vcpu: virtual cpu diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c index 0243b6e38d36..be042865d8a1 100644 --- a/arch/s390/kvm/gaccess.c +++ b/arch/s390/kvm/gaccess.c @@ -1161,6 +1161,107 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra, return rc; } +/** + * cmpxchg_guest_abs_with_key() - Perform cmpxchg on guest absolute address. + * @kvm: Virtual machine instance. + * @gpa: Absolute guest address of the location to be changed. + * @len: Operand length of the cmpxchg, required: 1 <= len <= 16. Providing a + * non power of two will result in failure. + * @old_p: Pointer to old value. If the location at @gpa contains this value, the + * exchange will succeed. After calling cmpxchg_guest_abs_with_key() *@old + * contains the value at @gpa before the attempt to exchange the value. + * @new: The value to place at @gpa. + * @access_key: The access key to use for the guest access. + * + * Atomically exchange the value at @gpa by @new, if it contains *@old. + * Honors storage keys. + * + * Return: * 0: successful exchange + * * 1: exchange unsuccessful + * * a program interruption code indicating the reason cmpxchg could + * not be attempted + * * -EINVAL: address misaligned or len not power of two + * * -EAGAIN: transient failure (len 1 or 2) + */ +int cmpxchg_guest_abs_with_key(struct kvm *kvm, gpa_t gpa, int len, + __uint128_t *old_p, __uint128_t new, + u8 access_key) +{ + gfn_t gfn = gpa >> PAGE_SHIFT; + struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); + bool writable; + hva_t hva; + int ret; + + if (!IS_ALIGNED(gpa, len)) + return -EINVAL; + + hva = gfn_to_hva_memslot_prot(slot, gfn, &writable); + if (kvm_is_error_hva(hva)) + return PGM_ADDRESSING; + /* + * Check if it's a read-only memslot, even though that cannot occur + * since those are unsupported. + * Don't try to actually handle that case. + */ + if (!writable) + return -EOPNOTSUPP; + + hva += offset_in_page(gpa); + switch (len) { + case 1: { + u8 old; + + ret = cmpxchg_user_key((u8 *)hva, &old, *old_p, new, access_key); + ret = ret < 0 ? ret : old != *old_p; + *old_p = old; + break; + } + case 2: { + u16 old; + + ret = cmpxchg_user_key((u16 *)hva, &old, *old_p, new, access_key); + ret = ret < 0 ? ret : old != *old_p; + *old_p = old; + break; + } + case 4: { + u32 old; + + ret = cmpxchg_user_key((u32 *)hva, &old, *old_p, new, access_key); + ret = ret < 0 ? ret : old != *old_p; + *old_p = old; + break; + } + case 8: { + u64 old; + + ret = cmpxchg_user_key((u64 *)hva, &old, *old_p, new, access_key); + ret = ret < 0 ? ret : old != *old_p; + *old_p = old; + break; + } + case 16: { + __uint128_t old; + + ret = cmpxchg_user_key((__uint128_t *)hva, &old, *old_p, new, access_key); + ret = ret < 0 ? ret : old != *old_p; + *old_p = old; + break; + } + default: + return -EINVAL; + } + mark_page_dirty_in_slot(kvm, slot, gfn); + /* + * Assume that the fault is caused by protection, either key protection + * or user page write protection. + */ + if (ret == -EFAULT) + ret = PGM_PROTECTION; + return ret; +} + /** * guest_translate_address_with_key - translate guest logical into guest absolute address * @vcpu: virtual cpu diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 45d4b8182b07..2410b4044283 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -576,7 +576,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_S390_VCPU_RESETS: case KVM_CAP_SET_GUEST_DEBUG: case KVM_CAP_S390_DIAG318: - case KVM_CAP_S390_MEM_OP_EXTENSION: r = 1; break; case KVM_CAP_SET_GUEST_DEBUG2: @@ -590,6 +589,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_S390_MEM_OP: r = MEM_OP_MAX_SIZE; break; + case KVM_CAP_S390_MEM_OP_EXTENSION: + /* + * Flag bits indicating which extensions are supported. + * The first extension doesn't use a flag, but pretend it does, + * this way that can be changed in the future. + */ + r = 0x3; + break; case KVM_CAP_NR_VCPUS: case KVM_CAP_MAX_VCPUS: case KVM_CAP_MAX_VCPU_ID: @@ -2714,12 +2721,19 @@ static bool access_key_invalid(u8 access_key) static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) { void __user *uaddr = (void __user *)mop->buf; + void __user *old_p = (void __user *)mop->old_p; + union { + __uint128_t quad; + char raw[sizeof(__uint128_t)]; + } old = { .quad = 0}, new = { .quad = 0 }; + unsigned int off_in_quad = sizeof(__uint128_t) - mop->size; u64 supported_flags; void *tmpbuf = NULL; int r, srcu_idx; supported_flags = KVM_S390_MEMOP_F_SKEY_PROTECTION - | KVM_S390_MEMOP_F_CHECK_ONLY; + | KVM_S390_MEMOP_F_CHECK_ONLY + | KVM_S390_MEMOP_F_CMPXCHG; if (mop->flags & ~supported_flags || !mop->size) return -EINVAL; if (mop->size > MEM_OP_MAX_SIZE) @@ -2741,6 +2755,15 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) } else { mop->key = 0; } + if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) { + if (mop->size > sizeof(new)) + return -EINVAL; + /* off_in_quad has been validated */ + if (copy_from_user(&new.raw[off_in_quad], uaddr, mop->size)) + return -EFAULT; + if (copy_from_user(&old.raw[off_in_quad], old_p, mop->size)) + return -EFAULT; + } if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) { tmpbuf = vmalloc(mop->size); if (!tmpbuf) @@ -2771,6 +2794,14 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) case KVM_S390_MEMOP_ABSOLUTE_WRITE: { if (mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY) { r = check_gpa_range(kvm, mop->gaddr, mop->size, GACC_STORE, mop->key); + } else if (mop->flags & KVM_S390_MEMOP_F_CMPXCHG) { + r = cmpxchg_guest_abs_with_key(kvm, mop->gaddr, mop->size, + &old.quad, new.quad, mop->key); + if (r == 1) { + r = KVM_S390_MEMOP_R_NO_XCHG; + if (copy_to_user(old_p, &old.raw[off_in_quad], mop->size)) + r = -EFAULT; + } } else { if (copy_from_user(tmpbuf, uaddr, mop->size)) { r = -EFAULT;
User space can use the MEM_OP ioctl to make storage key checked reads and writes to the guest, however, it has no way of performing atomic, key checked, accesses to the guest. Extend the MEM_OP ioctl in order to allow for this, by adding a cmpxchg mode. For now, support this mode for absolute accesses only. This mode can be use, for example, to set the device-state-change indicator and the adapter-local-summary indicator atomically. Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> --- include/uapi/linux/kvm.h | 5 ++ arch/s390/kvm/gaccess.h | 3 ++ arch/s390/kvm/gaccess.c | 101 +++++++++++++++++++++++++++++++++++++++ arch/s390/kvm/kvm-s390.c | 35 +++++++++++++- 4 files changed, 142 insertions(+), 2 deletions(-)