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 61c08aa9606d4e48a8a50639c956448a720174c3 upstream.
The vCPU-run asm blob does a manual comparison of a VMCS' launched status 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].
Originally, 'launched' was of type 'int' and so the asm blob used 'cmpl' to check the launch status. When 'launched' was moved to be stored on a per-VMCS basis, struct vcpu_vmx's "temporary" __launched flag was added in order to avoid having to pass the current VMCS into the asm blob. The new '__launched' was defined as a 'bool' and not an 'int', but the 'cmp' instruction was not updated.
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: d462b8192368 ("KVM: VMX: Keep list of loaded VMCSs, instead of vcpus") 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/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6399,7 +6399,7 @@ static void __vmx_vcpu_run(struct kvm_vc "mov %%" _ASM_AX", %%cr2 \n\t" "3: \n\t" /* Check if vmlaunch or vmresume is needed */ - "cmpl $0, %c[launched](%%" _ASM_CX ") \n\t" + "cmpb $0, %c[launched](%%" _ASM_CX ") \n\t" /* Load guest registers. Don't clobber flags. */ "mov %c[rax](%%" _ASM_CX "), %%" _ASM_AX " \n\t" "mov %c[rbx](%%" _ASM_CX "), %%" _ASM_BX " \n\t"