linux-kernel - Re: [PATCH v2 16/23] x86,vmx: Provide asm-goto-output vmread

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Date:   Tue, 14 Dec 2021 23:46:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        mark.rutland@....com, dvyukov@...gle.com, pbonzini@...hat.com,
        mbenes@...e.cz
Subject: Re: [PATCH v2 16/23] x86,vmx: Provide asm-goto-output vmread

On Tue, Dec 14, 2021 at 06:44:48PM +0000, Sean Christopherson wrote:

> This needs to route through a noinline vmread_error(), the intent is that KVM only
> does WARN once for all VMREAD failures, whereas having this inline will WARN once
> on each unique vmcs_read*().

Oh, fair enough.

> And at that point, we might as well hide the asm
> trampoline too.  The amount of ifdeffery gets a bit gross, but in for a penny in
> for a pound?
> 
> And like the other VMX instruction, I assume it's safe to annotate the failure
> path as instrumentation safe.
> 
> So this?

Yep, think so.

> ---
>  arch/x86/kvm/vmx/vmenter.S |  2 ++
>  arch/x86/kvm/vmx/vmx.c     |  7 +++++++
>  arch/x86/kvm/vmx/vmx_ops.h | 31 +++++++++++++++++++++++++++++++
>  3 files changed, 40 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
> index 3a6461694fc2..d8a7a0a69ec1 100644
> --- a/arch/x86/kvm/vmx/vmenter.S
> +++ b/arch/x86/kvm/vmx/vmenter.S
> @@ -238,6 +238,7 @@ SYM_FUNC_END(__vmx_vcpu_run)
> 
>  .section .text, "ax"
> 
> +#ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT

#ifndef ?

>  /**
>   * vmread_error_trampoline - Trampoline from inline asm to vmread_error()
>   * @field:	VMCS field encoding that failed