linux-kernel - Re: [RFC 6/7] x86/asm: Remap the TSS into the cpu entry area

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Date:   Mon, 13 Nov 2017 18:28:42 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Dave Hansen <dave.hansen@...el.com>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>
Subject: Re: [RFC 6/7] x86/asm: Remap the TSS into the cpu entry area

On Mon, Nov 13, 2017 at 6:25 PM, Andy Lutomirski <luto@...nel.org> wrote:
> On Mon, Nov 13, 2017 at 11:36 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> I forget what the actual size is, but aligning the hardware TSS struct
>> to 128 bytes might be sufficient. It's not that big.
>
> 104 bytes, so it's probably already fine.  For anything except an
> actual task switch, only the first 12 or so bytes matter.

Note that historically, about half of the Intel errata (that don't get
fixed) are about TSS in oddball situations, mainly page crossers.

I may be exaggerating just a tiny bit, but it's definitely a "don't do it".

               Linus