5.0-stable review patch. If anyone has any objections, please let me know.
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From: Sean Christopherson sean.j.christopherson@intel.com
commit 1ce072cbfd8dba46f117804850398e0b3040a541 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/vmx/nested.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -2765,7 +2765,7 @@ static int nested_vmx_check_vmentry_hw(s "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"