On Wed, Jan 02, 2019 at 03:26:30PM -0800, Sean Christopherson wrote: > On Wed, Jan 02, 2019 at 09:25:22PM +0200, Liran Alon wrote: > > Only 0 or all 1s can be written to IA32_MCG_CTL. > > SDM specifies other values as undefined and/or implementation specific. > > > > However, some guest kernels write different values. > > One such example is WinNT 4 SP6 which uses a value of 0xffffffff. > > > > Prefer to silently accept these writes to avoid an uncatched #GP in the guest. > > We will define our implementation specific behaviour as any value other than 0 > > to be treated as all 1s. > > I'm assuming this is a 32-bit guest, so what about going with a more > precise hackaround and explicitly allowing 0xffffffff for 32-bit guests, > e.g. sign-extending bit 31 when the value isn't already 0 or -1? > > It's worth keeping the #GP behavior for modern kernels, e.g. for testing > and debug. MSRs 0x0 and 0x1 are aliased to MSRs 0x400 and 0x401 for > historical reasons, i.e. WRMSR without setting ECX can easily write > MSR_IA32_MC0_CTL. Of course KVM probably doesn't emulate the aliasing so it'd likely #GP anyways, but I still think we should go with a more surgical hack :)
