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From:   Andy Lutomirski <luto@kernel.org>
Date:   Fri, 13 Jul 2018 10:19:16 -0700
Message-ID: <CALCETrUP1QUKPLPJg6_L5=Mzmq33cSvq+NMaYW01wTCepdjCyg@mail.gmail.com>
Subject: Re: [PATCH 03/39] x86/entry/32: Load task stack from x86_tss.sp1 in
 SYSENTER handler
To:     Joerg Roedel <joro@8bytes.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
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        Brian Gerst <brgerst@gmail.com>,
        David Laight <David.Laight@aculab.com>,
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        Eduardo Valentin <eduval@amazon.com>,
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        Hugh Dickins <hughd@google.com>,
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        Andrea Arcangeli <aarcange@redhat.com>,
        Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>,
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        Joerg Roedel <jroedel@suse.de>
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On Fri, Jul 13, 2018 at 2:48 AM, Joerg Roedel <joro@8bytes.org> wrote:
> On Thu, Jul 12, 2018 at 01:49:13PM -0700, Andy Lutomirski wrote:
>> > On Jul 11, 2018, at 4:29 AM, Joerg Roedel <joro@8bytes.org> wrote:
>> >    /* Offset from the sysenter stack to tss.sp0 */
>> > -    DEFINE(TSS_entry_stack, offsetof(struct cpu_entry_area, tss.x86_tss.sp0) -
>> > +    DEFINE(TSS_entry_stack, offsetof(struct cpu_entry_area, tss.x86_tss.sp1) -
>> >           offsetofend(struct cpu_entry_area, entry_stack_page.stack));
>> >
>>
>> The code reads differently. Did you perhaps mean TSS_task_stack?
>
> Well, the offset name came from TSS_sysenter_sp0, which was the offset
> from the sysenter_sp0 (==sysenter-stack) to the task stack in TSS, now
> sysenter_sp0 became entry_stack, because its used for all entry points
> and not only sysenter. So with the old convention the naming makes still
> sense, no?
>

Trying to parse it certainly makes my brain hurt a bit.  This is the
offset from the entry stack to sp1, where sp1 is the location of the
pointer to the task stack.

Maybe all the arithmetic could go in entry_32.S and the asm-offset
name could just be TSS_sp1, just like on 64-bit?

--Andy