Re: [PATCH v4] riscv: mm: Avoid spurious fault after hotplugging vmemmap

From: Andrew Morton <akpm@linux-foundation.org>
To: Vivian Wang <wangruikang@iscas.ac.cn>
Cc: Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Alexandre Ghiti <alex@ghiti.fr>,
	David Hildenbrand <david@kernel.org>,
	Lorenzo Stoakes <ljs@kernel.org>,
	"Liam R. Howlett" <liam@infradead.org>,
	Vlastimil Babka <vbabka@kernel.org>,
	Mike Rapoport <rppt@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Michal Hocko <mhocko@suse.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH v4] riscv: mm: Avoid spurious fault after hotplugging vmemmap
Date: Tue, 30 Jun 2026 21:11:00 -0700	[thread overview]
Message-ID: <20260630211100.5c8f09c607595fbb5bca0a74@linux-foundation.org> (raw)
In-Reply-To: <20260630-mark-after-vmemmap-populate-v4-1-febbc15da028@iscas.ac.cn>

On Tue, 30 Jun 2026 15:51:59 +0800 Vivian Wang <wangruikang@iscas.ac.cn> wrote:

> section_activate() does not flush TLB after populating new vmemmap
> pages. On most architectures, this is okay. However it is a problem on
> RISC-V since there the TLB caching non-present entries is permitted,
> which causes spurious faults on some hardwares.
> 
> This seems to be most easily reproduced with DEBUG_VM=y and
> PAGE_POISONING=y, which causes these newly mapped struct pages to be
> poisoned i.e. written to immediately after mapping.
> 
> Add a hook vmemmap_populate_finalize() in __populate_section_memmap()
> after population, to allow architectures to handle such situations as
> needed. Then implement it on RISC-V to arrange for the existing
> exception handler code to deal with these faults if they happen.

Thanks, I'll get this into linux-next for some testing exposure.

I'd of course prefer that the riscv maintainers review and merge this,
or I can upstream it with their ack?

btw, AI review suggests that there's a missing barrier in there (a
pre-existing thing)

	https://sashiko.dev/#/patchset/20260630-mark-after-vmemmap-populate-v4-1-febbc15da028@iscas.ac.cn

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