From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v2] KVM: VMX: Improve handle_external_interrupt_irqoff inline assembly
Date: Mon, 27 Apr 2020 12:25:12 -0700 [thread overview]
Message-ID: <20200427192512.GT14870@linux.intel.com> (raw)
In-Reply-To: <20200426115255.305060-1-ubizjak@gmail.com>
On Sun, Apr 26, 2020 at 01:52:55PM +0200, Uros Bizjak wrote:
> Improve handle_external_interrupt_irqoff inline assembly in several ways:
> - use "n" operand constraint instead of "i" and remove
What's the motivation for using 'n'? The 'i' variant is much more common,
i.e. less likely to trip up readers.
$ git grep -E "\"i\"\s*\(" | wc -l
768
$ git grep -E "\"n\"\s*\(" | wc -l
11
> unneeded %c operand modifiers and "$" prefixes
> - use %rsp instead of _ASM_SP, since we are in CONFIG_X86_64 part
> - use $-16 immediate to align %rsp
Heh, this one depends on the reader, I find 0xfffffffffffffff0 to be much
more intuitive, though admittedly also far easier to screw up.
> - remove unneeded use of __ASM_SIZE macro
> - define "ss" named operand only for X86_64
>
> The patch introduces no functional changes.
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> ---
> arch/x86/kvm/vmx/vmx.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index c2c6335a998c..7471f1b948b3 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6283,13 +6283,13 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
>
> asm volatile(
> #ifdef CONFIG_X86_64
> - "mov %%" _ASM_SP ", %[sp]\n\t"
> - "and $0xfffffffffffffff0, %%" _ASM_SP "\n\t"
> - "push $%c[ss]\n\t"
> + "mov %%rsp, %[sp]\n\t"
> + "and $-16, %%rsp\n\t"
> + "push %[ss]\n\t"
> "push %[sp]\n\t"
> #endif
> "pushf\n\t"
> - __ASM_SIZE(push) " $%c[cs]\n\t"
> + "push %[cs]\n\t"
> CALL_NOSPEC
> :
> #ifdef CONFIG_X86_64
> @@ -6298,8 +6298,10 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
> ASM_CALL_CONSTRAINT
> :
> [thunk_target]"r"(entry),
> - [ss]"i"(__KERNEL_DS),
> - [cs]"i"(__KERNEL_CS)
> +#ifdef CONFIG_X86_64
> + [ss]"n"(__KERNEL_DS),
> +#endif
> + [cs]"n"(__KERNEL_CS)
> );
>
> kvm_after_interrupt(vcpu);
> --
> 2.25.3
>
next prev parent reply other threads:[~2020-04-27 19:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-26 11:52 [PATCH v2] KVM: VMX: Improve handle_external_interrupt_irqoff inline assembly Uros Bizjak
2020-04-27 19:25 ` Sean Christopherson [this message]
2020-04-27 20:08 ` Uros Bizjak
2020-04-27 22:30 ` Sean Christopherson
2020-04-28 12:31 ` Uros Bizjak
2020-04-28 13:48 ` Paolo Bonzini
2020-05-03 22:23 ` Uros Bizjak
2020-05-03 23:08 ` Uros Bizjak
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