linux-kernel - [PATCH] KVM: VMX: Access @flags as a 32-bit value in __vmx_vcpu

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Date:   Sat, 19 Nov 2022 00:37:47 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>
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 <adobriyan@...il.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 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