Messages in this thread | | | Date | Thu, 29 Jun 2023 09:50:34 -0700 | Subject | Re: [PATCH 08/12] KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD} enabled" | From | Sean Christopherson <> |
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On Wed, Feb 22, 2023, Sean Christopherson wrote: > +Maxim > > On Wed, Feb 22, 2023, Yu Zhang wrote: > I'll opportunistically massage the comment to make it more explicit about why > VMLOAD needs to be intercepted. > > That said, clearing the bits for this seems wrong. That would corrupt the MSRs > for 64-bit Intel guests. The "target" of the fix was 32-bit L2s, i.e. I doubt > anything would notice. > > This patch fixes nested migration of 32 bit nested guests, that was > broken because incorrect cached values of SYSENTER msrs were stored in > the migration stream if L1 changed these msrs with > vmload prior to L2 entry.
Aha! Finally figured out what this code is doing. KVM intercepts VMLOAD so that KVM can correctly model the VMLOAD behavior of dropping bits 63:32, i.e. to clear svm->sysenter_eip_hi and svm->sysenter_esp_hi.
So the code is correct. I'll add this comment:
/* * Intercept VMLOAD if the vCPU mode is Intel in order to emulate that * VMLOAD drops bits 63:32 of SYSENTER (ignoring the fact that exposing * SVM on Intel is bonkers and extremely unlikely to work). */
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