On Fri, 2022-07-15 at 23:18 +0000, Sean Christopherson wrote: > On Fri, Jul 15, 2022, Jim Mattson wrote: > > 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? > > Then KVM (and probably many other things in the kernel) is hosed. The same argument > (that KVM isn't paranoid enough) can likely be made for a number of MSRs and critical > registers. > I was thinking about the same thing and I also 100% agree with the above. Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> Best regards, Maxim Levitsky
