On Wed, Feb 07, 2024, Xin Li wrote: > @@ -7382,6 +7419,24 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu, > > vmx_disable_fb_clear(vmx); > > + /* > + * %cr2 needs to be saved after a VM exit and restored before a VM > + * entry in case a VM exit happens immediately after delivery of a > + * guest #PF but before guest reads %cr2. > + * > + * A FRED guest should read its #PF faulting linear address from > + * the event data field in its FRED stack frame instead of %cr2. > + * But the FRED 5.0 spec still requires a FRED CPU to update %cr2 > + * in the normal way, thus %cr2 is still updated even for a FRED > + * guest. > + * > + * Note, an NMI could interrupt KVM: > + * 1) after VM exit but before CR2 is saved. > + * 2) after CR2 is restored but before VM entry. > + * And a #PF could happen durng NMI handlng, which overwrites %cr2. > + * Thus exc_nmi() should save and restore %cr2 upon entering and > + * before leaving to make sure %cr2 not corrupted. > + */ This is 99.9% noise. What software does or does not do with respect to CR2 is completely irrelevant. The *only* thing that matters is the architectural behavior, and architecturally guest CR2 _must_ be up-to-date at all times because CR2 accesses cannot be intercepted. So, just say: /* * Note, even though FRED delivers the faulting linear address via the * event data field on the stack, CR2 is still updated. */ > if (vcpu->arch.cr2 != native_read_cr2()) > native_write_cr2(vcpu->arch.cr2); >
