KVM: nSVM: Fail emulation of VMRUN/VMLOAD/VMSAVE if mapping vmcb12 fails

KVM: nSVM: Fail emulation of VMRUN/VMLOAD/VMSAVE if mapping vmcb12 fails

KVM currently injects a #GP if mapping vmcb12 fails when emulating
VMRUN/VMLOAD/VMSAVE. This is not architectural behavior, as #GP should
only be injected if the physical address is not supported or not
aligned. Instead, handle it as an emulation failure, similar to how nVMX
handles failures to read/write guest memory in several emulation paths.

When virtual VMLOAD/VMSAVE is enabled, if vmcb12's GPA is not mapped in
the NPTs a VMEXIT(#NPF) will be generated, and KVM will install an MMIO
SPTE and emulate the instruction if there is no corresponding memslot.
x86_emulate_insn() will return EMULATION_FAILED as VMLOAD/VMSAVE are not
handled as part of the twobyte_insn cases.

Even though this will also result in an emulation failure, it will only
result in a straight return to userspace if
KVM_CAP_EXIT_ON_EMULATION_FAILURE is set. Otherwise, it would inject #UD
and only exit to userspace if not in guest mode. So the behavior is
slightly different if virtual VMLOAD/VMSAVE is enabled.

Fixes: 3d6368ef580a ("KVM: SVM: Add VMRUN handler")
Reported-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260316202732.3164936-8-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>