diff options
| author | Sean Christopherson <sean.j.christopherson@intel.com> | 2019-01-25 07:40:49 -0800 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2019-02-12 13:12:13 +0100 |
| commit | 1ce072cbfd8dba46f117804850398e0b3040a541 (patch) | |
| tree | a04e1fa9d3e8dcc5a6462352713f982501241b69 /arch/x86/kvm/vmx/nested.c | |
| parent | 61c08aa9606d4e48a8a50639c956448a720174c3 (diff) | |
KVM: nVMX: Check a single byte for VMCS "launched" in nested early checks
Nested early checks does a manual comparison of a VMCS' launched status
in its asm blob to execute the correct VM-Enter instruction, i.e.
VMLAUNCH vs. VMRESUME. The launched flag is a bool, which is a typedef
of _Bool. C99 does not define an exact size for _Bool, stating only
that is must be large enough to hold '0' and '1'. Most, if not all,
compilers use a single byte for _Bool, including gcc[1].
The use of 'cmpl' instead of 'cmpb' was not deliberate, but rather the
result of a copy-paste as the asm blob was directly derived from the asm
blob for vCPU-run.
This has not caused any known problems, likely due to compilers aligning
variables to 4-byte or 8-byte boundaries and KVM zeroing out struct
vcpu_vmx during allocation. I.e. vCPU-run accesses "junk" data, it just
happens to always be zero and so doesn't affect the result.
[1] https://gcc.gnu.org/ml/gcc-patches/2000-10/msg01127.html
Fixes: 52017608da33 ("KVM: nVMX: add option to perform early consistency checks via H/W")
Cc: <stable@vger.kernel.org>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/vmx/nested.c')
| -rw-r--r-- | arch/x86/kvm/vmx/nested.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index d8ea4ebd79e7..50c9e04910ea 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -2761,7 +2761,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu) "add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */ /* Check if vmlaunch or vmresume is needed */ - "cmpl $0, %c[launched](%% " _ASM_CX")\n\t" + "cmpb $0, %c[launched](%% " _ASM_CX")\n\t" "call vmx_vmenter\n\t" |