KVM: x86: Update comments about MSR lists exposed to userspace
Commit Message
Refresh comments about msrs_to_save, emulated_msrs, and msr_based_features
to remove stale references left behind by commit 2374b7310b66 (KVM:
x86/pmu: Use separate array for defining "PMU MSRs to save"), and to
better reflect the current reality, e.g. emulated_msrs is no longer just
for MSRs that are "kvm-specific".
Reported-by: Binbin Wu <binbin.wu@linux.intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
base-commit: 31b4fc3bc64aadd660c5bfa5178c86a7ba61e0f7
Comments
On 6/7/2023 8:46 AM, Sean Christopherson wrote:
> Refresh comments about msrs_to_save, emulated_msrs, and msr_based_features
> to remove stale references left behind by commit 2374b7310b66 (KVM:
> x86/pmu: Use separate array for defining "PMU MSRs to save"), and to
> better reflect the current reality, e.g. emulated_msrs is no longer just
> for MSRs that are "kvm-specific".
>
> Reported-by: Binbin Wu <binbin.wu@linux.intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/x86.c | 27 +++++++++++++--------------
> 1 file changed, 13 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5ad55ef71433..c77f72cf6dc8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1427,15 +1427,14 @@ int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu)
> EXPORT_SYMBOL_GPL(kvm_emulate_rdpmc);
>
> /*
> - * List of msr numbers which we expose to userspace through KVM_GET_MSRS
> - * and KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST.
> - *
> - * The three MSR lists(msrs_to_save, emulated_msrs, msr_based_features)
> - * extract the supported MSRs from the related const lists.
> - * msrs_to_save is selected from the msrs_to_save_all to reflect the
> - * capabilities of the host cpu. This capabilities test skips MSRs that are
> - * kvm-specific. Those are put in emulated_msrs_all; filtering of emulated_msrs
> - * may depend on host virtualization features rather than host cpu features.
> + * The three MSR lists(msrs_to_save, emulated_msrs, msr_based_features) track
> + * the set of MSRs that KVM exposes to userspace through KVM_GET_MSRS,
> + * KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST. msrs_to_save holds MSRs that
> + * require host support, i.e. should be probed via RDMSR. emulated_msrs holds
> + * MSRs that emulates without strictly requiring host support.
emulates -> emulate/emulated?
BTW, do you think is it better to use msrs_emulated instead of
emulated_msrs to align the naming style?
> + * msr_based_features holds MSRs that enumerate features, i.e. are effectively
> + * CPUID leafs. Note, msr_based_features isn't mutually exclusive with
> + * msrs_to_save and emulated_msrs.
> */
>
> static const u32 msrs_to_save_base[] = {
> @@ -1531,11 +1530,11 @@ static const u32 emulated_msrs_all[] = {
> MSR_IA32_UCODE_REV,
>
> /*
> - * The following list leaves out MSRs whose values are determined
> - * by arch/x86/kvm/vmx/nested.c based on CPUID or other MSRs.
> - * We always support the "true" VMX control MSRs, even if the host
> - * processor does not, so I am putting these registers here rather
> - * than in msrs_to_save_all.
> + * KVM always supports the "true" VMX control MSRs, even if the host
> + * does not. The VMX MSRs as a whole are considered "emulated" as KVM
> + * doesn't strictly require them to exist in the host (ignoring that
> + * KVM would refuse to load in the first place if the core set of MSRs
> + * aren't supported).
> */
> MSR_IA32_VMX_BASIC,
> MSR_IA32_VMX_TRUE_PINBASED_CTLS,
>
> base-commit: 31b4fc3bc64aadd660c5bfa5178c86a7ba61e0f7
On Wed, Jun 07, 2023, Binbin Wu wrote:
>
>
> On 6/7/2023 8:46 AM, Sean Christopherson wrote:
> > Refresh comments about msrs_to_save, emulated_msrs, and msr_based_features
> > to remove stale references left behind by commit 2374b7310b66 (KVM:
> > x86/pmu: Use separate array for defining "PMU MSRs to save"), and to
> > better reflect the current reality, e.g. emulated_msrs is no longer just
> > for MSRs that are "kvm-specific".
> >
> > Reported-by: Binbin Wu <binbin.wu@linux.intel.com>
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> > arch/x86/kvm/x86.c | 27 +++++++++++++--------------
> > 1 file changed, 13 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 5ad55ef71433..c77f72cf6dc8 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1427,15 +1427,14 @@ int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu)
> > EXPORT_SYMBOL_GPL(kvm_emulate_rdpmc);
> > /*
> > - * List of msr numbers which we expose to userspace through KVM_GET_MSRS
> > - * and KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST.
> > - *
> > - * The three MSR lists(msrs_to_save, emulated_msrs, msr_based_features)
> > - * extract the supported MSRs from the related const lists.
> > - * msrs_to_save is selected from the msrs_to_save_all to reflect the
> > - * capabilities of the host cpu. This capabilities test skips MSRs that are
> > - * kvm-specific. Those are put in emulated_msrs_all; filtering of emulated_msrs
> > - * may depend on host virtualization features rather than host cpu features.
> > + * The three MSR lists(msrs_to_save, emulated_msrs, msr_based_features) track
> > + * the set of MSRs that KVM exposes to userspace through KVM_GET_MSRS,
> > + * KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST. msrs_to_save holds MSRs that
> > + * require host support, i.e. should be probed via RDMSR. emulated_msrs holds
> > + * MSRs that emulates without strictly requiring host support.
> emulates -> emulate/emulated?
Ah, no, that's supposed to be "that KVM emulates". I'll fix that up when applying.
> BTW, do you think is it better to use msrs_emulated instead of emulated_msrs
> to align the naming style?
No, "emulated" is used as an adjective that describes each MSR, versus the "to save"
part of msrs_to_save being a description of the list, not each MSR.
If I were going to rename anything, it would be msr_based_features, because that
reads as "MSR-based features", i.e. reads as "a list of features that are tied
to MSRs", whereas the list actually tracks "feature-based MSRs", i.e. "a list of
MSRs that track features".
On Tue, 06 Jun 2023 17:46:36 -0700, Sean Christopherson wrote:
> Refresh comments about msrs_to_save, emulated_msrs, and msr_based_features
> to remove stale references left behind by commit 2374b7310b66 (KVM:
> x86/pmu: Use separate array for defining "PMU MSRs to save"), and to
> better reflect the current reality, e.g. emulated_msrs is no longer just
> for MSRs that are "kvm-specific".
>
>
> [...]
Applied to kvm-x86 misc, thanks!
[1/1] KVM: x86: Update comments about MSR lists exposed to userspace
https://github.com/kvm-x86/linux/commit/a30642570855
--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes
@@ -1427,15 +1427,14 @@ int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu)
EXPORT_SYMBOL_GPL(kvm_emulate_rdpmc);
/*
- * List of msr numbers which we expose to userspace through KVM_GET_MSRS
- * and KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST.
- *
- * The three MSR lists(msrs_to_save, emulated_msrs, msr_based_features)
- * extract the supported MSRs from the related const lists.
- * msrs_to_save is selected from the msrs_to_save_all to reflect the
- * capabilities of the host cpu. This capabilities test skips MSRs that are
- * kvm-specific. Those are put in emulated_msrs_all; filtering of emulated_msrs
- * may depend on host virtualization features rather than host cpu features.
+ * The three MSR lists(msrs_to_save, emulated_msrs, msr_based_features) track
+ * the set of MSRs that KVM exposes to userspace through KVM_GET_MSRS,
+ * KVM_SET_MSRS, and KVM_GET_MSR_INDEX_LIST. msrs_to_save holds MSRs that
+ * require host support, i.e. should be probed via RDMSR. emulated_msrs holds
+ * MSRs that emulates without strictly requiring host support.
+ * msr_based_features holds MSRs that enumerate features, i.e. are effectively
+ * CPUID leafs. Note, msr_based_features isn't mutually exclusive with
+ * msrs_to_save and emulated_msrs.
*/
static const u32 msrs_to_save_base[] = {
@@ -1531,11 +1530,11 @@ static const u32 emulated_msrs_all[] = {
MSR_IA32_UCODE_REV,
/*
- * The following list leaves out MSRs whose values are determined
- * by arch/x86/kvm/vmx/nested.c based on CPUID or other MSRs.
- * We always support the "true" VMX control MSRs, even if the host
- * processor does not, so I am putting these registers here rather
- * than in msrs_to_save_all.
+ * KVM always supports the "true" VMX control MSRs, even if the host
+ * does not. The VMX MSRs as a whole are considered "emulated" as KVM
+ * doesn't strictly require them to exist in the host (ignoring that
+ * KVM would refuse to load in the first place if the core set of MSRs
+ * aren't supported).
*/
MSR_IA32_VMX_BASIC,
MSR_IA32_VMX_TRUE_PINBASED_CTLS,