| Message ID | 20201203171118.372391-1-mlevitsk@redhat.com |
|---|---|
| Headers | show |
| Series | RFC: Precise TSC migration | expand |
On Thu, Dec 03, 2020 at 07:11:15PM +0200, Maxim Levitsky wrote: > Hi! > > This is the second version of the work to make TSC migration more accurate, > as was defined by Paulo at: > https://www.spinics.net/lists/kvm/msg225525.html Maxim, Can you please make a description of what is the practical problem that is being fixed, preferably with instructions on how to reproduce ? > I omitted most of the semi-offtopic points I raised related to TSC > in the previous RFC where we can continue the discussion. > > I do want to raise another thing that I almost forgot. > > On AMD systems, the Linux kernel will mark the guest tsc as > unstable unless invtsc is set which is set on recent AMD > hardware. > > Take a look at 'unsynchronized_tsc()' to verify this. > > This is another thing that IMHO should be fixed at least when > running under KVM. > > Note that I forgot to mention that > X86_FEATURE_TSC_RELIABLE also short-circuits this code, > thus giving another reason to enable it under KVM. > > Changes from V1: > > - added KVM_TSC_STATE_TIMESTAMP_VALID instead of testing ns == 0 > - allow diff < 0, because it is still better that capping it to 0 > - updated tsc_msr_test unit test to cover this feature > - refactoring > > Patches to enable this feature in qemu are in the process of > being sent to qemu-devel mailing list. > > Best regards, > Maxim Levitsky > > Maxim Levitsky (3): > KVM: x86: implement KVM_{GET|SET}_TSC_STATE > KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS > kvm/selftests: update tsc_msrs_test to cover > KVM_X86_QUIRK_TSC_HOST_ACCESS > > Documentation/virt/kvm/api.rst | 65 +++++++++++++ > arch/x86/include/uapi/asm/kvm.h | 1 + > arch/x86/kvm/x86.c | 92 ++++++++++++++++++- > include/uapi/linux/kvm.h | 15 +++ > .../selftests/kvm/x86_64/tsc_msrs_test.c | 79 ++++++++++++++-- > 5 files changed, 237 insertions(+), 15 deletions(-) > > -- > 2.26.2 >
I'm queueing patches 2 and 3 for now, since the sane MSR interface is a prerequisite anyway. Paolo On 03/12/20 18:11, Maxim Levitsky wrote: > Hi! > > This is the second version of the work to make TSC migration more accurate, > as was defined by Paulo at: > https://www.spinics.net/lists/kvm/msg225525.html > > I omitted most of the semi-offtopic points I raised related to TSC > in the previous RFC where we can continue the discussion. > > I do want to raise another thing that I almost forgot. > > On AMD systems, the Linux kernel will mark the guest tsc as > unstable unless invtsc is set which is set on recent AMD > hardware. > > Take a look at 'unsynchronized_tsc()' to verify this. > > This is another thing that IMHO should be fixed at least when > running under KVM. > > Note that I forgot to mention that > X86_FEATURE_TSC_RELIABLE also short-circuits this code, > thus giving another reason to enable it under KVM. > > Changes from V1: > > - added KVM_TSC_STATE_TIMESTAMP_VALID instead of testing ns == 0 > - allow diff < 0, because it is still better that capping it to 0 > - updated tsc_msr_test unit test to cover this feature > - refactoring > > Patches to enable this feature in qemu are in the process of > being sent to qemu-devel mailing list. > > Best regards, > Maxim Levitsky > > Maxim Levitsky (3): > KVM: x86: implement KVM_{GET|SET}_TSC_STATE > KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS > kvm/selftests: update tsc_msrs_test to cover > KVM_X86_QUIRK_TSC_HOST_ACCESS > > Documentation/virt/kvm/api.rst | 65 +++++++++++++ > arch/x86/include/uapi/asm/kvm.h | 1 + > arch/x86/kvm/x86.c | 92 ++++++++++++++++++- > include/uapi/linux/kvm.h | 15 +++ > .../selftests/kvm/x86_64/tsc_msrs_test.c | 79 ++++++++++++++-- > 5 files changed, 237 insertions(+), 15 deletions(-) >
Hi! This is the second version of the work to make TSC migration more accurate, as was defined by Paulo at: https://www.spinics.net/lists/kvm/msg225525.html I omitted most of the semi-offtopic points I raised related to TSC in the previous RFC where we can continue the discussion. I do want to raise another thing that I almost forgot. On AMD systems, the Linux kernel will mark the guest tsc as unstable unless invtsc is set which is set on recent AMD hardware. Take a look at 'unsynchronized_tsc()' to verify this. This is another thing that IMHO should be fixed at least when running under KVM. Note that I forgot to mention that X86_FEATURE_TSC_RELIABLE also short-circuits this code, thus giving another reason to enable it under KVM. Changes from V1: - added KVM_TSC_STATE_TIMESTAMP_VALID instead of testing ns == 0 - allow diff < 0, because it is still better that capping it to 0 - updated tsc_msr_test unit test to cover this feature - refactoring Patches to enable this feature in qemu are in the process of being sent to qemu-devel mailing list. Best regards, Maxim Levitsky Maxim Levitsky (3): KVM: x86: implement KVM_{GET|SET}_TSC_STATE KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS kvm/selftests: update tsc_msrs_test to cover KVM_X86_QUIRK_TSC_HOST_ACCESS Documentation/virt/kvm/api.rst | 65 +++++++++++++ arch/x86/include/uapi/asm/kvm.h | 1 + arch/x86/kvm/x86.c | 92 ++++++++++++++++++- include/uapi/linux/kvm.h | 15 +++ .../selftests/kvm/x86_64/tsc_msrs_test.c | 79 ++++++++++++++-- 5 files changed, 237 insertions(+), 15 deletions(-) -- 2.26.2