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). */
