On Wed, Jun 04, 2025, Paolo Bonzini wrote:
> On 5/30/25 01:39, Sean Christopherson wrote:
> > Use a dedicated array of MSRPM offsets to merge L0 and L1 bitmaps, i.e. to
> > merge KVM's vmcb01 bitmap with L1's vmcb12 bitmap. This will eventually
> > allow for the removal of direct_access_msrs, as the only path where
> > tracking the offsets is truly justified is the merge for nested SVM, where
> > merging in chunks is an easy way to batch uaccess reads/writes.
> >
> > Opportunistically omit the x2APIC MSRs from the merge-specific array
> > instead of filtering them out at runtime.
> >
> > Note, disabling interception of XSS, EFER, PAT, GHCB, and TSC_AUX is
> > mutually exclusive with nested virtualization, as KVM passes through the
> > MSRs only for SEV-ES guests, and KVM doesn't support nested virtualization
> > for SEV+ guests. Defer removing those MSRs to a future cleanup in order
> > to make this refactoring as benign as possible.
> >
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/svm/nested.c | 72 +++++++++++++++++++++++++++++++++------
> > arch/x86/kvm/svm/svm.c | 4 +++
> > arch/x86/kvm/svm/svm.h | 2 ++
> > 3 files changed, 67 insertions(+), 11 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index 89a77f0f1cc8..e53020939e60 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -184,6 +184,64 @@ void recalc_intercepts(struct vcpu_svm *svm)
> > }
> > }
> > +static int nested_svm_msrpm_merge_offsets[9] __ro_after_init;
> > +static int nested_svm_nr_msrpm_merge_offsets __ro_after_init;
> > +
> > +int __init nested_svm_init_msrpm_merge_offsets(void)
> > +{
> > + const u32 merge_msrs[] = {
>
> "static const", please.
Ugh, I was thinking the compiler would be magical enough to not generate code to
fill an on-stack array at runtime, but that's not the case.
AFAICT, tagging it __initdata works, so I'll do this to hopefully ensure the
memory is discarded after module load.
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index fb4808cf4711..af530f45bf64 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -205,7 +205,7 @@ static int svm_msrpm_offset(u32 msr)
int __init nested_svm_init_msrpm_merge_offsets(void)
{
- const u32 merge_msrs[] = {
+ static const u32 __initdata merge_msrs[] = {
MSR_STAR,
MSR_IA32_SYSENTER_CS,
MSR_IA32_SYSENTER_EIP,
