linux-kernel - Re: [PATCH v2 5/7] x86/mm, tracing: Fix CR2 corruption

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Date:   Sun, 7 Jul 2019 12:44:02 +0900
From:   Eiichi Tsukata <devel@...ukata.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        He Zhe <zhe.he@...driver.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v2 5/7] x86/mm, tracing: Fix CR2 corruption



On 2019/07/07 7:27, Steven Rostedt wrote:

> 
> We also have to deal with reading vmalloc'd data as that can fault too.
> The perf ring buffer IIUC is vmalloc, so if perf records in one of
> these locations, then the reading of the vmalloc area has a potential
> to fault corrupting the CR2 register as well. Or have we changed
> vmalloc to no longer fault?
> 
> -- Steve
> 

It seems that perf ring buffer does not normally use vmalloc.
It depends on CONFIG_PERF_USE_VMALLOC introduced by the following commit:

commit 906010b2134e14a2e377decbadd357b3d0ab9c6a
Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date:   Mon Sep 21 16:08:49 2009 +0200

    perf_event: Provide vmalloc() based mmap() backing
    
    Some architectures such as Sparc, ARM and MIPS (basically
    everything with flush_dcache_page()) need to deal with dcache
    aliases by carefully placing pages in both kernel and user maps.
    
    These architectures typically have to use vmalloc_user() for this.
    
    However, on other architectures, vmalloc() is not needed and has
    the downsides of being more restricted and slower than regular
    allocations.
    
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
    Acked-by: David Miller <davem@...emloft.net>
    Cc: Andrew Morton <akpm@...ux-foundation.org>
    Cc: Jens Axboe <jens.axboe@...cle.com>
    Cc: Paul Mackerras <paulus@...ba.org>
    LKML-Reference: <1254830228.21044.272.camel@...top>
    Signed-off-by: Ingo Molnar <mingo@...e.hu>