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Date: Wed, 1 Nov 2017 11:23:46 +0100
From: Borislav Petkov <bp@suse.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Brian Gerst <brgerst@gmail.com>, Dave Hansen <dave.hansen@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 17/18] x86/asm/64: Remove thread_struct::sp0
Message-ID: <20171101102346.vnv3bdncc6p7ke3e@pd.tnic>
References: <cover.1509006199.git.luto@kernel.org>
 <7272938bf9f494d73f3061a052e194f763c99ce2.1509006199.git.luto@kernel.org>
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On Thu, Oct 26, 2017 at 01:26:49AM -0700, Andy Lutomirski wrote:
> On x86_64, we can easily calculate sp0 when needed instead of
> storing it in thread_struct.
> 
> On x86_32, a similar cleanup would be possible, but it would require
> cleaning up the vm86 code first, and that can wait for a later
> cleanup series.
> 
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

...

> @@ -816,23 +825,6 @@ static inline void spin_lock_prefetch(const void *x)
>  	.addr_limit		= KERNEL_DS,				  \
>  }
>  
> -/*
> - * TOP_OF_KERNEL_STACK_PADDING reserves 8 bytes on top of the ring0 stack.
> - * This is necessary to guarantee that the entire "struct pt_regs"
> - * is accessible even if the CPU haven't stored the SS/ESP registers
> - * on the stack (interrupt gate does not save these registers
> - * when switching to the same priv ring).
> - * Therefore beware: accessing the ss/esp fields of the
> - * "struct pt_regs" is possible, but they may contain the
> - * completely wrong values.
> - */

Why are we removing the explaination of TOP_OF_KERNEL_STACK_PADDING? Is
that going to change later?

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--