linux-kernel - Re: [PATCH 5/7] x86: Use IBRS for firmware update path

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Date:   Fri, 5 Jan 2018 14:40:32 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        linux-kernel@...r.kernel.org, David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH 5/7] x86: Use IBRS for firmware update path

On Thu, 4 Jan 2018, Tim Chen wrote:
>  #ifdef APM_ZERO_SEGS
>  #	define APM_DO_ZERO_SEGS \
>  		"pushl %%ds\n\t" \
> @@ -28,6 +30,7 @@ static inline void apm_bios_call_asm(u32 func, u32 ebx_in, u32 ecx_in,
>  					u32 *eax, u32 *ebx, u32 *ecx,
>  					u32 *edx, u32 *esi)
>  {
> +	unprotected_firmware_begin();
>  	/*
>  	 * N.B. We do NOT need a cld after the BIOS call
>  	 * because we always save and restore the flags.
> @@ -44,6 +47,7 @@ static inline void apm_bios_call_asm(u32 func, u32 ebx_in, u32 ecx_in,
>  		  "=S" (*esi)
>  		: "a" (func), "b" (ebx_in), "c" (ecx_in)
>  		: "memory", "cc");
> +	unprotected_formware_end();

This doesn't even compile unless the new compiler speculates that into
unprotected_firmware_end().

Thanks,

	tglx