linux-kernel - Re: [PATCH V3 0/3] x86/entry: simply stack switching when exception on userspace

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Date:   Mon, 17 Aug 2020 13:31:18 +0800
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        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 V3 0/3] x86/entry: simply stack switching when exception
 on userspace


Deeply sorry, the cover-letter was forgotten to send to LKML.

Here it is:

On 2020/8/17 14:23, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@...ux.alibaba.com>
> 
> 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 2-3 simplify stack switching for .Lerror_bad_iret by just doing
> all the work in one function (fixup_bad_iret()).
> 
> The patch set is based on v5.9-rc1
> 
> Changed from V1:
> 	based on tip/master -> based on tip/x86/entry
> 
> 	patch 1 replaces the patch1,2 of V1, it borrows the
> 	original interrupt_entry's code into error_entry.
> 
> 	patch2-4 is V1's patch3-5, unchanged (but rebased)
> 
> Changed from V2:
> 	(re-)based on v5.9-rc1
> 	drop the patch4 of V2 patchset
> 
> Cc: Andy Lutomirski <luto@...nel.org>,
> Cc: Thomas Gleixner <tglx@...utronix.de>,
> Cc: Ingo Molnar <mingo@...hat.com>,
> Cc: Borislav Petkov <bp@...en8.de>,
> Cc: x86@...nel.org,
> Cc: "H. Peter Anvin" <hpa@...or.com>,
> Cc: Peter Zijlstra <peterz@...radead.org>,
> Cc: Alexandre Chartre <alexandre.chartre@...cle.com>,
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
> Cc: Jann Horn <jannh@...gle.com>,
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> 
> Lai Jiangshan (3):
>    x86/entry: avoid calling into sync_regs() when entering from userspace
>    x86/entry: directly switch to kernel stack when .Lerror_bad_iret
>    x86/entry: remove unused sync_regs()
> 
>   arch/x86/entry/entry_64.S    | 52 +++++++++++++++++++++++-------------
>   arch/x86/include/asm/traps.h |  1 -
>   arch/x86/kernel/traps.c      | 22 +++------------
>   3 files changed, 38 insertions(+), 37 deletions(-)
>