KVM: SVM: Disable SEV-ES support if MMIO caching is disable

Disable SEV-ES if MMIO caching is disabled as SEV-ES relies on MMIO SPTEs
generating #NPF(RSVD), which are reflected by the CPU into the guest as
a #VC.  With SEV-ES, the untrusted host, a.k.a. KVM, doesn't have access
to the guest instruction stream or register state and so can't directly
emulate in response to a #NPF on an emulated MMIO GPA.  Disabling MMIO
caching means guest accesses to emulated MMIO ranges cause #NPF(!PRESENT),
and those flavors of #NPF cause automatic VM-Exits, not #VC.

Adjust KVM's MMIO masks to account for the C-bit location prior to doing
SEV(-ES) setup, and document that dependency between adjusting the MMIO
SPTE mask and SEV(-ES) setup.

Fixes: b09763da4dd8 ("KVM: x86/mmu: Add module param to disable MMIO caching (for testing)")
Reported-by: Michael Roth <[email protected]>
Tested-by: Michael Roth <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: [email protected]
Signed-off-by: Sean Christopherson <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

0 files changed, 0 insertions, 0 deletions