From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Uros Bizjak <ubizjak@gmail.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: SVM/VMX: Use %rax instead of %__ASM_AX within CONFIG_X86_64
Date: Wed, 12 May 2021 15:27:29 +0000 [thread overview]
Message-ID: <YJvz4crhU7Gbn0p0@google.com> (raw)
In-Reply-To: <074223fd-6f82-9ed6-8664-f324f5027da5@redhat.com>
On Wed, May 12, 2021, Paolo Bonzini wrote:
> On 12/05/21 13:21, Uros Bizjak wrote:
> > There is no need to use %__ASM_AX within CONFIG_X86_64. The macro
> > will always expand to %rax.
> > diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
> > index 3a6461694fc2..9273709e4800 100644
> > --- a/arch/x86/kvm/vmx/vmenter.S
> > +++ b/arch/x86/kvm/vmx/vmenter.S
> > @@ -142,14 +142,14 @@ SYM_FUNC_START(__vmx_vcpu_run)
> > mov VCPU_RSI(%_ASM_AX), %_ASM_SI
> > mov VCPU_RDI(%_ASM_AX), %_ASM_DI
> > #ifdef CONFIG_X86_64
> > - mov VCPU_R8 (%_ASM_AX), %r8
> > - mov VCPU_R9 (%_ASM_AX), %r9
> > - mov VCPU_R10(%_ASM_AX), %r10
> > - mov VCPU_R11(%_ASM_AX), %r11
> > - mov VCPU_R12(%_ASM_AX), %r12
> > - mov VCPU_R13(%_ASM_AX), %r13
> > - mov VCPU_R14(%_ASM_AX), %r14
> > - mov VCPU_R15(%_ASM_AX), %r15
> > + mov VCPU_R8 (%rax), %r8
> > + mov VCPU_R9 (%rax), %r9
> > + mov VCPU_R10(%rax), %r10
> > + mov VCPU_R11(%rax), %r11
> > + mov VCPU_R12(%rax), %r12
> > + mov VCPU_R13(%rax), %r13
> > + mov VCPU_R14(%rax), %r14
> > + mov VCPU_R15(%rax), %r15
> > #endif
> > /* Load guest RAX. This kills the @regs pointer! */
> > mov VCPU_RAX(%_ASM_AX), %_ASM_AX
> > @@ -175,14 +175,14 @@ SYM_FUNC_START(__vmx_vcpu_run)
> > mov %_ASM_SI, VCPU_RSI(%_ASM_AX)
> > mov %_ASM_DI, VCPU_RDI(%_ASM_AX)
> > #ifdef CONFIG_X86_64
> > - mov %r8, VCPU_R8 (%_ASM_AX)
> > - mov %r9, VCPU_R9 (%_ASM_AX)
> > - mov %r10, VCPU_R10(%_ASM_AX)
> > - mov %r11, VCPU_R11(%_ASM_AX)
> > - mov %r12, VCPU_R12(%_ASM_AX)
> > - mov %r13, VCPU_R13(%_ASM_AX)
> > - mov %r14, VCPU_R14(%_ASM_AX)
> > - mov %r15, VCPU_R15(%_ASM_AX)
> > + mov %r8, VCPU_R8 (%rax)
> > + mov %r9, VCPU_R9 (%rax)
> > + mov %r10, VCPU_R10(%rax)
> > + mov %r11, VCPU_R11(%rax)
> > + mov %r12, VCPU_R12(%rax)
> > + mov %r13, VCPU_R13(%rax)
> > + mov %r14, VCPU_R14(%rax)
> > + mov %r15, VCPU_R15(%rax)
> > #endif
> > /* Clear RAX to indicate VM-Exit (as opposed to VM-Fail). */
> >
>
> It looks a bit weird either way (either the address is different within the
> #ifdef, or the address is different from the destinatino), so I lean more
> towards avoiding churn.
Even though it's unnecessary, I prefer %_ASM_AX since it provides a consistent
flow across the 64-bit-only boundary.
prev parent reply other threads:[~2021-05-12 16:02 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 11:21 [PATCH] KVM: SVM/VMX: Use %rax instead of %__ASM_AX within CONFIG_X86_64 Uros Bizjak
2021-05-12 11:58 ` Paolo Bonzini
2021-05-12 15:27 ` Sean Christopherson [this message]
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