On Fri, Jul 15, 2022 at 4:02 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > Reject KVM if entry '0' in the host's IA32_PAT MSR is not programmed to > writeback (WB) memtype. KVM subtly relies on IA32_PAT entry '0' to be > programmed to WB by leaving the PAT bits in shadow paging and NPT SPTEs > as '0'. If something other than WB is in PAT[0], at _best_ guests will > suffer very poor performance, and at worst KVM will crash the system by > breaking cache-coherency expecations (e.g. using WC for guest memory). > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- What if someone changes the host's PAT to violate this rule *after* kvm is loaded?
