Inject #UD when emulating XSETBV if CR4.OSXSAVE is not set. This also
covers the "XSAVE not supported" check, as setting CR4.OSXSAVE=1 #GPs if
XSAVE is not supported (and userspace gets to keep the pieces if it
forces incoherent vCPU state).
Add a comment to kvm_emulate_xsetbv() to call out that the CPU checks
CR4.OSXSAVE before checking for intercepts. AMD'S APM implies that #UD
has priority (says that intercepts are checked before #GP exceptions),
while Intel's SDM says nothing about interception priority. However,
testing on hardware shows that both AMD and Intel CPUs prioritize the #UD
over interception.
Fixes: 02d4160fbd ("x86: KVM: add xsetbv to the emulator")
Cc: stable@vger.kernel.org
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220824033057.3576315-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
50b2d49baf