2022-11-19 01:54:37

by Sean Christopherson

Subject: [PATCH] KVM: VMX: Access @flags as a 32-bit value in __vmx_vcpu_run()

Access @flags using 32-bit operands when saving and testing @flags for
VMX_RUN_VMRESUME, as using 8-bit operands is unnecessarily fragile due
to relying on VMX_RUN_VMRESUME being in bits 0-7. The behavior of
treating @flags a single byte is a holdover from when the param was
"bool launched", i.e. is not deliberate.

Cc: Alexey Dobriyan <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/vmx/vmenter.S | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 0b5db4de4d09..5bd39f63497d 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -69,8 +69,8 @@ SYM_FUNC_START(__vmx_vcpu_run)
*/
push %_ASM_ARG2

- /* Copy @flags to BL, _ASM_ARG3 is volatile. */
- mov %_ASM_ARG3B, %bl
+ /* Copy @flags to EBX, _ASM_ARG3 is volatile. */
+ mov %_ASM_ARG3L, %ebx

lea (%_ASM_SP), %_ASM_ARG2
call vmx_update_host_rsp
@@ -106,7 +106,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
mov (%_ASM_SP), %_ASM_AX

/* Check if vmlaunch or vmresume is needed */
- testb $VMX_RUN_VMRESUME, %bl
+ test $VMX_RUN_VMRESUME, %ebx

/* Load guest registers. Don't clobber flags. */
mov VCPU_RCX(%_ASM_AX), %_ASM_CX
@@ -128,7 +128,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
/* Load guest RAX. This kills the @regs pointer! */
mov VCPU_RAX(%_ASM_AX), %_ASM_AX

- /* Check EFLAGS.ZF from 'testb' above */
+ /* Check EFLAGS.ZF from 'test VMX_RUN_VMRESUME' above */
jz .Lvmlaunch

/*

base-commit: d663b8a285986072428a6a145e5994bc275df994
--
2.38.1.584.g0f3c55d4c2-goog

2022-11-19 03:28:29

by Jim Mattson

Subject: Re: [PATCH] KVM: VMX: Access @flags as a 32-bit value in __vmx_vcpu_run()

On Fri, Nov 18, 2022 at 5:33 PM Sean Christopherson <[email protected]> wrote:
>
> Access @flags using 32-bit operands when saving and testing @flags for
> VMX_RUN_VMRESUME, as using 8-bit operands is unnecessarily fragile due
> to relying on VMX_RUN_VMRESUME being in bits 0-7. The behavior of
> treating @flags a single byte is a holdover from when the param was
> "bool launched", i.e. is not deliberate.
>
> Cc: Alexey Dobriyan <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
Reviewed-by: Jim Mattson <[email protected]>

2023-01-19 21:14:54

by Sean Christopherson

Subject: Re: [PATCH] KVM: VMX: Access @flags as a 32-bit value in __vmx_vcpu_run()

On Sat, 19 Nov 2022 00:37:47 +0000, Sean Christopherson wrote:
> Access @flags using 32-bit operands when saving and testing @flags for
> VMX_RUN_VMRESUME, as using 8-bit operands is unnecessarily fragile due
> to relying on VMX_RUN_VMRESUME being in bits 0-7. The behavior of
> treating @flags a single byte is a holdover from when the param was
> "bool launched", i.e. is not deliberate.
>
>
> [...]

Applied to kvm-x86 vmx, thanks!

[1/1] KVM: VMX: Access @flags as a 32-bit value in __vmx_vcpu_run()
https://github.com/kvm-x86/linux/commit/55de8353fc67

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes