KVM: x86: nSVM: Redirect IA32_PAT accesses to either hPAT or gPAT

When handling PAT accesses from L2, route PAT accesses to either hPAT or
gPAT based on whether or not L2 has a separate PAT, i.e. if KVM is actually
emulating gPAT, instead of using L1's PAT for everything.  Specifically, if
KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled, the vCPU is in guest mode
with nested NPT enabled, *and* the access if from the guest (i.e. is not
from the host stuffing PAT as part of save/restore), then redirect guest
PAT accesses to the gPAT "register" in vmcb02, i.e. emulate gPAT for L2.

Always route non-guest accesses to hPAT, i.e. L1's PAT in vcpu->arch.pat,
to ensures that KVM_{G,S}ET_MSRS and KVM_{G,S}ET_NESTED_STATE are
independent of each other and can be ordered arbitrarily during save and
restore.  E.g. if KVM didn't exempt host accesses, then whether a write to
PAT hit hPAT or gPAT would vary based on whether userspace restores PAT
before or after nested state.  Note, gPAT is saved and restored separately
via KVM_{G,S}ET_NESTED_STATE.

WARN if there's a host-initiated access to PAT from within KVM_RUN, i.e. if
KVM itself initiated the access, as there are no such accesses today, and
it's not clear what the "right" behavior would be.

Fixes: 15038e147247 ("KVM: SVM: obey guest PAT")
Signed-off-by: Jim Mattson <jmattson@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions