linux-kernel - Re: [PATCH v3 2/3] x86/entry: Clear registers for 64bit exceptions/interrupts

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Message-ID: <20180206090455.GA15925@isilmar-4.linta.de>
Date:   Tue, 6 Feb 2018 10:04:55 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     tglx@...utronix.de, mingo@...nel.org,
        Andi Kleen <ak@...ux.intel.com>, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, luto@...nel.org
Subject: Re: [PATCH v3 2/3] x86/entry: Clear registers for 64bit
 exceptions/interrupts

On Mon, Feb 05, 2018 at 05:18:11PM -0800, Dan Williams wrote:
> @@ -1178,6 +1180,7 @@ ENTRY(paranoid_entry)
>  	cld
>  	SAVE_C_REGS 8
>  	SAVE_EXTRA_REGS 8
> +	CLEAR_REGS_NOSPEC
>  	ENCODE_FRAME_POINTER 8
>  	movl	$1, %ebx
>  	movl	$MSR_GS_BASE, %ecx
> @@ -1185,7 +1188,6 @@ ENTRY(paranoid_entry)
>  	testl	%edx, %edx
>  	js	1f				/* negative -> in kernel */
>  	SWAPGS
> -	xorl	%ebx, %ebx

Here, %ebx will be filled with $1 (see code snipped above) *after* the
call to CLEAR_REGS_NOSPEC. That's what this line has been clearing in the
past. So I'm not sure whether this line should be removed.

Thanks,
	Dominik