diff options
| author | Oliver Upton <oupton@google.com> | 2022-03-16 00:55:37 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-04-02 05:41:10 -0400 |
| commit | f1a9761fbb00639c5e73835f7f373ef834bb867f (patch) | |
| tree | 423a1f817617a7cc72d059ab2a83639469a7034f /Documentation/virt | |
| parent | c15e0ae42c8e5a61e9aca8aac920517cf7b3e94e (diff) | |
KVM: x86: Allow userspace to opt out of hypercall patching
KVM handles the VMCALL/VMMCALL instructions very strangely. Even though
both of these instructions really should #UD when executed on the wrong
vendor's hardware (i.e. VMCALL on SVM, VMMCALL on VMX), KVM replaces the
guest's instruction with the appropriate instruction for the vendor.
Nonetheless, older guest kernels without commit c1118b3602c2 ("x86: kvm:
use alternatives for VMCALL vs. VMMCALL if kernel text is read-only")
do not patch in the appropriate instruction using alternatives, likely
motivating KVM's intervention.
Add a quirk allowing userspace to opt out of hypercall patching. If the
quirk is disabled, KVM synthesizes a #UD in the guest.
Signed-off-by: Oliver Upton <oupton@google.com>
Message-Id: <20220316005538.2282772-2-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index d13fa6600467..700df350332b 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7134,6 +7134,15 @@ The valid bits in cap.args[0] are: Additionally, when this quirk is disabled, KVM clears CPUID.01H:ECX[bit 3] if IA32_MISC_ENABLE[bit 18] is cleared. + + KVM_X86_QUIRK_FIX_HYPERCALL_INSN By default, KVM rewrites guest + VMMCALL/VMCALL instructions to match the + vendor's hypercall instruction for the + system. When this quirk is disabled, KVM + will no longer rewrite invalid guest + hypercall instructions. Executing the + incorrect hypercall instruction will + generate a #UD within the guest. =================================== ============================================ 8. Other capabilities. |