| Message ID | 20220903012849.938069-4-vannapurve@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | Execute hypercalls from guests according to cpu type | expand |
Please use "KVM: selftest: ..." for the shortlog. On Sat, Sep 03, 2022 at 01:28:47AM +0000, Vishal Annapurve wrote: > Modify following APIs for x86 implementation: > 1) kvm_arch_main : Query the cpu vendor and cache the value in advance. > 2) kvm_arch_post_vm_load: Populate cpu type in the guest memory so that > guest doesn't need to execute cpuid instruction again. This commit message only describes a subset of the changes in this commit, and does not provide any context on why the changes are being made (other than a clue about avoiding CPUID). I also think this could be split up into 2 separate commits. I would suggest first patch changes is_{intel,amd}_cpu() to return a cached result. e.g. KVM: selftests: Precompute the result for is_{intel,amd}_cpu() Cache the vendor CPU type in a global variable so that multiple calls to is_intel_cpu() do not need to re-execute CPUID. This will be useful in a follow-up commit to check if running on AMD or Intel from within a selftest guest where executing CPUID requires a VM-exit. Then add support for AMD to kvm_hypercall(): KVM: selftests: Add AMD support to kvm_hypercall() Add support for AMD hypercalls to kvm_hypercall() so that it can be used in selftests running on Intel or AMD hosts. This will be used in a follow up commit to ... As part of this change, sync the global variable is_cpu_amd into the guest so the guest can determine which hypercall instruction to use without needing to re-execute CPUID for every hypercall. > > Suggested-by: Sean Christopherson <seanjc@google.com> > Signed-off-by: Vishal Annapurve <vannapurve@google.com> > --- > .../testing/selftests/kvm/lib/x86_64/processor.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c > index e22cfc4bf284..ac104653ab43 100644 > --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c > +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c > @@ -19,6 +19,7 @@ > #define MAX_NR_CPUID_ENTRIES 100 > > vm_vaddr_t exception_handlers; > +static int is_cpu_amd = -1; Should this just be a bool? Since you are initializing it before main(), there is really no way for any code to observe it's pre-initialized value. And nothing even checks if is_cpu_amd -1, it just silently returns false from is_intel_cpu() and is_amd_cpu(). > > static void regs_dump(FILE *stream, struct kvm_regs *regs, uint8_t indent) > { > @@ -1019,7 +1020,7 @@ static bool cpu_vendor_string_is(const char *vendor) > > bool is_intel_cpu(void) > { > - return cpu_vendor_string_is("GenuineIntel"); > + return (is_cpu_amd == 0); > } > > /* > @@ -1027,7 +1028,7 @@ bool is_intel_cpu(void) > */ > bool is_amd_cpu(void) > { > - return cpu_vendor_string_is("AuthenticAMD"); > + return (is_cpu_amd == 1); > } > > void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits) > @@ -1182,9 +1183,15 @@ uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2, > { > uint64_t r; > > - asm volatile("vmcall" > + if (is_amd_cpu()) > + asm volatile("vmmcall" > : "=a"(r) > : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3)); > + else > + asm volatile("vmcall" > + : "=a"(r) > + : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3)); > + > return r; > } > > @@ -1314,8 +1321,10 @@ bool vm_is_unrestricted_guest(struct kvm_vm *vm) > > void kvm_arch_main(void) > { > + is_cpu_amd = cpu_vendor_string_is("AuthenticAMD") ? 1 : 0; > } > > void kvm_arch_post_vm_load(struct kvm_vm *vm) > { > + sync_global_to_guest(vm, is_cpu_amd); > } > -- > 2.37.2.789.g6183377224-goog >
On Thu, Sep 08, 2022 at 03:54:41PM -0700, David Matlack wrote:
> Please use "KVM: selftest: ..." for the shortlog.
Doh. "KVM: selftests: ..."
On Thu, Sep 8, 2022 at 3:54 PM David Matlack <dmatlack@google.com> wrote: > > Please use "KVM: selftest: ..." for the shortlog. > Ack. > On Sat, Sep 03, 2022 at 01:28:47AM +0000, Vishal Annapurve wrote: > > Modify following APIs for x86 implementation: > > 1) kvm_arch_main : Query the cpu vendor and cache the value in advance. > > 2) kvm_arch_post_vm_load: Populate cpu type in the guest memory so that > > guest doesn't need to execute cpuid instruction again. > > This commit message only describes a subset of the changes in this > commit, and does not provide any context on why the changes are being > made (other than a clue about avoiding CPUID). > > I also think this could be split up into 2 separate commits. > Ack, will add more details to the commit log. Though since is_amd_cpu/is_intel_cpu is used by both selftest VMM and selftest guest logic, I would prefer to not split this change into two. For now, I will upload the series with this change being a single patch. We can discuss again if this split is really needed. Regards, Vishal > I would suggest first patch changes is_{intel,amd}_cpu() to return a cached > result. e.g. > > KVM: selftests: Precompute the result for is_{intel,amd}_cpu() > > Cache the vendor CPU type in a global variable so that multiple calls > to is_intel_cpu() do not need to re-execute CPUID. This will be useful > in a follow-up commit to check if running on AMD or Intel from within > a selftest guest where executing CPUID requires a VM-exit. > > Then add support for AMD to kvm_hypercall(): > > KVM: selftests: Add AMD support to kvm_hypercall() > > Add support for AMD hypercalls to kvm_hypercall() so that it can be > used in selftests running on Intel or AMD hosts. This will be used in > a follow up commit to ... > > As part of this change, sync the global variable is_cpu_amd into the > guest so the guest can determine which hypercall instruction to use > without needing to re-execute CPUID for every hypercall. >
diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c index e22cfc4bf284..ac104653ab43 100644 --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c @@ -19,6 +19,7 @@ #define MAX_NR_CPUID_ENTRIES 100 vm_vaddr_t exception_handlers; +static int is_cpu_amd = -1; static void regs_dump(FILE *stream, struct kvm_regs *regs, uint8_t indent) { @@ -1019,7 +1020,7 @@ static bool cpu_vendor_string_is(const char *vendor) bool is_intel_cpu(void) { - return cpu_vendor_string_is("GenuineIntel"); + return (is_cpu_amd == 0); } /* @@ -1027,7 +1028,7 @@ bool is_intel_cpu(void) */ bool is_amd_cpu(void) { - return cpu_vendor_string_is("AuthenticAMD"); + return (is_cpu_amd == 1); } void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits) @@ -1182,9 +1183,15 @@ uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2, { uint64_t r; - asm volatile("vmcall" + if (is_amd_cpu()) + asm volatile("vmmcall" : "=a"(r) : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3)); + else + asm volatile("vmcall" + : "=a"(r) + : "a"(nr), "b"(a0), "c"(a1), "d"(a2), "S"(a3)); + return r; } @@ -1314,8 +1321,10 @@ bool vm_is_unrestricted_guest(struct kvm_vm *vm) void kvm_arch_main(void) { + is_cpu_amd = cpu_vendor_string_is("AuthenticAMD") ? 1 : 0; } void kvm_arch_post_vm_load(struct kvm_vm *vm) { + sync_global_to_guest(vm, is_cpu_amd); }
Modify following APIs for x86 implementation: 1) kvm_arch_main : Query the cpu vendor and cache the value in advance. 2) kvm_arch_post_vm_load: Populate cpu type in the guest memory so that guest doesn't need to execute cpuid instruction again. Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Vishal Annapurve <vannapurve@google.com> --- .../testing/selftests/kvm/lib/x86_64/processor.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)