linux-kernel - Re: [PATCH v4 2/2] mm: use clear_user_(high)page() for arch with special user folio handling

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Message-ID: <673d05d5-276d-4b65-941c-6c9295e276b1@suse.cz>
Date: Mon, 9 Dec 2024 19:12:30 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: David Hildenbrand <david@...hat.com>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Miaohe Lin <linmiaohe@...wei.com>, Kefeng Wang <wangkefeng.wang@...wei.com>,
 John Hubbard <jhubbard@...dia.com>,
 "Huang, Ying" <ying.huang@...ux.alibaba.com>,
 Ryan Roberts <ryan.roberts@....com>, Alexander Potapenko
 <glider@...gle.com>, Kees Cook <keescook@...omium.org>,
 Vineet Gupta <vgupta@...nel.org>, linux-kernel@...r.kernel.org,
 linux-snps-arc@...ts.infradead.org,
 Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v4 2/2] mm: use clear_user_(high)page() for arch with
 special user folio handling

On 12/7/24 18:16, Zi Yan wrote:
> Some architectures have special handling after clearing user folios:
> architectures, which set cpu_dcache_is_aliasing() to true, require
> flushing dcache; arc, which sets cpu_icache_is_aliasing() to true, changes
> folio->flags to make icache coherent to dcache. So __GFP_ZERO using only
> clear_page() is not enough to zero user folios and clear_user_(high)page()
> must be used. Otherwise, user data will be corrupted.
> 
> Fix it by always clearing user folios with clear_user_(high)page() when
> cpu_dcache_is_aliasing() is true or cpu_icache_is_aliasing() is true.
> Rename alloc_zeroed() to alloc_need_zeroing() and invert the logic to
> clarify its intend.

user_alloc_needs_zeroing() would be perhaps more descriptive?

> Fixes: 5708d96da20b ("mm: avoid zeroing user movable page twice with init_on_alloc=1")
> Reported-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Closes: https://lore.kernel.org/linux-mm/CAMuHMdV1hRp_NtR5YnJo=HsfgKQeH91J537Gh4gKk3PFZhSkbA@mail.gmail.com/
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Signed-off-by: Zi Yan <ziy@...dia.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>