linux-kernel - Re: [PATCH 03/39] x86/entry/32: Load task stack from x86

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Message-Id: <823BAA9B-FACA-4E91-BE56-315FF569297C@amacapital.net>
Date:   Thu, 12 Jul 2018 13:49:13 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>, jroedel@...e.de
Subject: Re: [PATCH 03/39] x86/entry/32: Load task stack from x86_tss.sp1 in SYSENTER handler



> On Jul 11, 2018, at 4:29 AM, Joerg Roedel <joro@...tes.org> wrote:
> 
> From: Joerg Roedel <jroedel@...e.de>
> We want x86_tss.sp0 point to the entry stack later to use
> it as a trampoline stack for other kernel entry points
> besides SYSENTER.

Makes sense: sp0 will be the entry stack. But:

> 
> 
>    /* 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?

Also, the “top of task stack” is a bit weird on 32-bit due to vm86. Can you document *exactly* what goes in sp1?