linux-kernel - Re: [PATCH] powerpc/mm: Don't kmap_atomic() in pte_offset

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Message-Id: <48YT3X0KXSz9sPJ@ozlabs.org>
Date:   Fri,  6 Mar 2020 11:27:51 +1100 (AEDT)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/mm: Don't kmap_atomic() in pte_offset_map() on PPC32

On Mon, 2020-02-17 at 09:41:35 UTC, Christophe Leroy wrote:
> On PPC32, pte_offset_map() does a kmap_atomic() in order to support
> page tables allocated in high memory, just like ARM and x86/32.
> 
> But since at least 2008 and commit 8054a3428fbe ("powerpc: Remove dead
> CONFIG_HIGHPTE"), page tables are never allocated in high memory.
> 
> When the page is in low mem, kmap_atomic() just returns the page
> address but still disable preemption and pagefault. And it is
> not an inlined function, so we suffer function call for no reason.
> 
> Make pte_offset_map() the same as pte_offset_kernel() and make
> pte_unmap() void, in the same way as PPC64 which doesn't have HIGHMEM.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/6453f9ed9d4e4b4cdf201bf34bf460c436bf50ea

cheers