linux-kernel - Re: [PATCH v9 09/12] mm/kasan: kasan specific map populate function

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Date:   Mon, 9 Oct 2017 15:07:01 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Will Deacon <will.deacon@....com>
Cc:     Mark Rutland <mark.rutland@....com>, catalin.marinas@....com,
        linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, kasan-dev@...glegroups.com, borntraeger@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net,
        willy@...radead.org, mhocko@...nel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>, sam@...nborg.org,
        mgorman@...hsingularity.net,
        Steve Sistare <steven.sistare@...cle.com>,
        daniel.m.jordan@...cle.com, bob.picco@...cle.com
Subject: Re: [PATCH v9 09/12] mm/kasan: kasan specific map populate function

>
> Ok, but I'm still missing why you think that is needed. What would be the
> second page table walker that needs implementing?
>
> I guess we could implement that on arm64 using our current vmemmap_populate
> logic and an explicit memset.
>

Hi Will,

What do you mean by explicit memset()? We can't simply memset() from
start to end without doing the page table walk, because at the time
kasan is calling vmemmap_populate() we have a tmp_pg_dir instead of
swapper_pg_dir.

We could do the explicit memset() after
cpu_replace_ttbr1(lm_alias(swapper_pg_dir)); but again, this was in
one of my previous implementations, and I was asked to replace that.

Pavel