On Thu, May 18, 2023, Binbin Wu wrote:
> msrs_to_save_all is out-dated after commit 2374b7310b66
> (KVM: x86/pmu: Use separate array for defining "PMU MSRs to save").
>
> Update the comments to msrs_to_save_base.
>
> Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ceb7c5e9cf9e..ca7cff5252ae 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1432,7 +1432,7 @@ EXPORT_SYMBOL_GPL(kvm_emulate_rdpmc);
> *
> * 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
> + * msrs_to_save is selected from the msrs_to_save_base to reflect the
A straight conversion isn't correct, msrs_to_save isn't selected from *just*
msrs_to_save_base.
> * 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
This "kvm-specific" blurb is also stale.
> * may depend on host virtualization features rather than host cpu features.
> @@ -1535,7 +1535,7 @@ static const u32 emulated_msrs_all[] = {
> * 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.
> + * than in msrs_to_save_base.
And this entire comment is rather weird, e.g. I have no idea what MSRs the part
about CPUID and other MSRs is referring to.
Rather than do a blind replacement, how about this?
--
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Date: Mon, 5 Jun 2023 12:56:46 -0700
Subject: [PATCH] KVM: x86: Update comments about MSR lists exposed to
userspace
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@xxxxxxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
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.
+ * 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
--
