[lkml]   [2019]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
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"

 \ /
  Last update: 2019-03-22 13:26    [W:1.282 / U:4.764 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site