linux-kernel - Re: [PATCH v2 6/6] x86/speculation: Use IBRS if available before calling into firmware

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Date:   Sun, 11 Feb 2018 12:46:43 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     David Woodhouse <dwmw@...zon.co.uk>
Cc:     tglx@...utronix.de, karahmed@...zon.de, sironi@...zon.de,
        x86@...nel.org, kvm@...r.kernel.org, torvalds@...ux-foundation.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org, bp@...en8.de,
        peterz@...radead.org, jmattson@...gle.com, rkrcmar@...hat.com,
        arjan.van.de.ven@...el.com, dave.hansen@...el.com
Subject: Re: [PATCH v2 6/6] x86/speculation: Use IBRS if available before
 calling into firmware


* David Woodhouse <dwmw@...zon.co.uk> wrote:

> Retpoline means the kernel is safe because it has no indirect branches.
> But firmware isn't, so use IBRS for firmware calls if it's available.

Ok, this approach looks good to me in principle, but:

> --- a/arch/x86/include/asm/apm.h
> +++ b/arch/x86/include/asm/apm.h
> @@ -7,6 +7,8 @@
>  #ifndef _ASM_X86_MACH_DEFAULT_APM_H
>  #define _ASM_X86_MACH_DEFAULT_APM_H
>  
> +#include <asm/spec_ctrl.h>

I cannot see this header file upstream anywhere, nor in any other patch in my mbox 
- is there some dependency that has to be applied first?

Thanks,

	Ingo