On Wed, Aug 31, 2022, Maxim Levitsky wrote: > On Wed, 2022-08-31 at 00:34 +0000, Sean Christopherson wrote: > > Remove SVM's so called "hybrid-AVIC mode" and reinstate the restriction > > where AVIC is disabled if x2APIC is enabled. The argument that the > > "guest is not supposed to access xAPIC mmio when uses x2APIC" is flat out > > wrong. Activating x2APIC completely disables the xAPIC MMIO region, > > there is nothing that says the guest must not access that address. > > > > Concretely, KVM-Unit-Test's existing "apic" test fails the subtests that > > expect accesses to the APIC base region to not be emulated when x2APIC is > > enabled. > > > > Furthermore, allowing the guest to trigger MMIO emulation in a mode where > > KVM doesn't expect such emulation to occur is all kinds of dangerous. > > > > Tweak the restriction so that it only inhibits AVIC if x2APIC is actually > > enabled instead of inhibiting AVIC is x2APIC is exposed to the guest. > > > > This reverts commit 0e311d33bfbef86da130674e8528cc23e6acfe16. > > I don't agree with this patch. > > When reviewing this code I did note that MMIO is left enabled which is kind > of errata on KVM side, and nobody objected to this. I didn't object because I didn't read the patch. I'm very much objecting now.
