linux-kernel - Re: [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and lm

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Date:   Thu, 1 Dec 2016 11:10:35 -0800
From:   Laura Abbott <labbott@...hat.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com
Subject: Re: [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and
 lm_alias

On 12/01/2016 03:36 AM, Andrey Ryabinin wrote:
> On 11/29/2016 09:55 PM, Laura Abbott wrote:
>> __pa_symbol is the correct API to find the physical address of symbols.
>> Switch to it to allow for debugging APIs to work correctly.
> 
> But __pa() is correct for symbols. I see how __pa_symbol() might be a little
> faster than __pa(), but there is nothing wrong in using __pa() on symbols.
> 
>> Other
>> functions such as p*d_populate may call __pa internally. Ensure that the
>> address passed is in the linear region by calling lm_alias.
> 
> Why it should be linear mapping address? __pa() translates kernel image address just fine.
> This lm_alias() only obfuscates source code. Generated code is probably worse too.
> 
> 

This is part of adding CONFIG_DEBUG_VIRTUAL for arm64. We want to
differentiate between __pa and __pa_symbol to enforce stronger
virtual checks and have __pa only be for linear map addresses.

Thanks,
Laura