linux-kernel - Re: [PATCH V3 3/7] x86/entry: Switch the stack after error

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Date:   Fri, 18 Mar 2022 12:12:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH V3 3/7] x86/entry: Switch the stack after error_entry()
 returns

On Thu, Mar 17, 2022 at 12:43:02AM +0800, Lai Jiangshan wrote:
> On Wed, Mar 16, 2022 at 11:05 PM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > >  SYM_CODE_END(error_entry)
> >
> > So the new Changelog doesn't seem to help me much. But looking at both
> > fixup_bad_iret() and sync_regs(), they both have:
> >
> >   __this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1
> 

Yes, I can't read :/ Functions don't both use that.

Your patch is correct, not switching the stack in between runs sync_regs
from another stack, but the end result should be the same.