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

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Message-ID: <20171009181433.wevxa447d4g6kdsj@dhcp22.suse.cz>
Date:   Mon, 9 Oct 2017 20:14:33 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     Will Deacon <will.deacon@....com>,
        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, 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

On Mon 09-10-17 13:51:47, Pavel Tatashin wrote:
> Hi Will,
> 
> I can go back to that approach, if Michal OK with it. But, that would
> mean that I would need to touch every single architecture that
> implements vmemmap_populate(), and also pass flags at least through
> these functions on every architectures (some have more than one
> decided by configs).:
> 
> vmemmap_populate()
> vmemmap_populate_basepages()
> vmemmap_populate_hugepages()
> vmemmap_pte_populate()
> __vmemmap_alloc_block_buf()
> alloc_block_buf()
> vmemmap_alloc_block()
> 
> IMO, while I understand that it looks strange that we must walk page
> table after creating it, it is a better approach: more enclosed as it
> effects kasan only, and more universal as it is in common code.

While I understand that gfp mask approach might look better at first
sight this is by no means a general purpose API so I would rather be
pragmatic and have a smaller code footprint than a more general
interface. Kasan is pretty much a special case and doing a one time
initialization 2 pass thing is imho acceptable. If this turns out to be
impractical in future then let's fix it up but right now I would rather
go a simpler path.
-- 
Michal Hocko
SUSE Labs