KVM: x86/mmu: Bug the VM, not the host kernel, if KVM write-protects upper SPTEs

KVM: x86/mmu: Bug the VM, not the host kernel, if KVM write-protects upper SPTEs

Instead of bugging the host kernel, WARN and terminate the VM if KVM
attempts to write-protect at a level that cannot use leaf SPTEs.
There is no reason to bring down the entire host; even termininating
the VM is likely overkill, but in theory a missed write could corrupt
guest memory, so play it safe.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20260618185641.2022368-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>