From: Sean Christopherson Date: Fri, 25 Jan 2019 15:40:49 +0000 (-0800) Subject: KVM: nVMX: Check a single byte for VMCS "launched" in nested early checks X-Git-Tag: v5.1-rc1~15^2~92 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=1ce072cbfd8dba46f117804850398e0b3040a541;p=linux.git 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: Reviewed-by: Jim Mattson Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini --- 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"