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Date:   Fri, 22 Mar 2019 12:17:31 +0100
From:   Greg Kroah-Hartman <>
Cc:     Greg Kroah-Hartman <>,, Jim Mattson <>,
        Konrad Rzeszutek Wilk <>,
        Sean Christopherson <>,
        Paolo Bonzini <>
Subject: [PATCH 5.0 232/238] KVM: nVMX: Check a single byte for VMCS "launched" in nested early checks

5.0-stable review patch.  If anyone has any objections, please let me know.


From: Sean Christopherson <>

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.


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 <>
Signed-off-by: Greg Kroah-Hartman <>

 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"

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