linux-kernel - Re: [PATCH 1/5] ioremap: Rework pXd_free_pYd

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Date:   Fri, 14 Sep 2018 20:36:24 +0000
From:   "Kani, Toshi" <toshi.kani@....com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "will.deacon@....com" <will.deacon@....com>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "cpandya@...eaurora.org" <cpandya@...eaurora.org>,
        "Hocko, Michal" <MHocko@...e.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/5] ioremap: Rework pXd_free_pYd_page() API

On Wed, 2018-09-12 at 11:26 +0100, Will Deacon wrote:
> The recently merged API for ensuring break-before-make on page-table
> entries when installing huge mappings in the vmalloc/ioremap region is
> fairly counter-intuitive, resulting in the arch freeing functions
> (e.g. pmd_free_pte_page()) being called even on entries that aren't
> present. This resulted in a minor bug in the arm64 implementation, giving
> rise to spurious VM_WARN messages.
> 
> This patch moves the pXd_present() checks out into the core code,
> refactoring the callsites at the same time so that we avoid the complex
> conjunctions when determining whether or not we can put down a huge
> mapping.
> 
> Cc: Chintan Pandya <cpandya@...eaurora.org>
> Cc: Toshi Kani <toshi.kani@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Will Deacon <will.deacon@....com>

Yes, this looks nicer.

Reviewed-by: Toshi Kani <toshi.kani@....com>

Thanks,
-Toshi