linux-kernel - Re: [PATCH V2 0/4] x86/entry: simply stack switching when exception on userspace

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Message-ID: <CAJhGHyBSzhm7h5dROAKSzdSD3czmUNG+80rS9tpaau_U23p4Ug@mail.gmail.com>
Date:   Tue, 16 Jun 2020 09:56:00 +0800
From:   Lai Jiangshan <jiangshanlai+lkml@...il.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jann Horn <jannh@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH V2 0/4] x86/entry: simply stack switching when exception
 on userspace

On Sat, May 30, 2020 at 2:33 AM Andy Lutomirski <luto@...nel.org> wrote:
>
> On Fri, May 29, 2020 at 1:26 AM Lai Jiangshan <laijs@...ux.alibaba.com> wrote:
> >
> > 7f2590a110b8("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")
> > has resulted that when exception on userspace, the kernel (error_entry)
> > always push the pt_regs to entry stack(sp0), and then copy them to the
> > kernel stack.
> >
> > And recent x86/entry work makes interrupt also use idtentry
> > and makes all the interrupt code save the pt_regs on the sp0 stack
> > and then copy it to the thread stack like exception.
> >
> > This is hot path (page fault, ipi), such overhead should be avoided.
> > And the original interrupt_entry directly switches to kernel stack
> > and pushes pt_regs to kernel stack. We should do it for error_entry.
> > This is the job of patch1.
> >
> > Patch 2-4 simply stack switching for .Lerror_bad_iret by just doing
> > all the work in one function (fixup_bad_iret()).
> >
> > The patch set is based on tip/x86/entry (28447ea41542) (May 20).
>
> There are definitely good cleanups in here, but I think it would be
> nice rebased to whatever lands in 5.8-rc1 settles.
>

Hello, All

This patchset can be smoothly applicable to the newest tip/x86/entry
which has 5.8-rc1 merged. Which means I don't have to respin/resend it
until any update is needed.

Could you have a review on it please.

Thanks
Lai