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Tue, 15 Sep 2026 13:43:23 +0000 X-Mizu-Trace-ID: abc51d4308209202 X-Migadu-Flow: FLOW_OUT Message-ID: <30bcc70c-be07-4237-9bb1-554aa5b5c5c2@linux.dev> Date: Tue, 15 Sep 2026 21:43:15 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/huge_memory: fix pgtable withdrawal for huge zero PMDs To: Andrew Morton , Kiryl Shutsemau , "David Hildenbrand (Arm)" Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, ljs@kernel.org, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260912234635.db50397364858aa15f58f4d7@linux-foundation.org> <20260913072312.52111-1-lance.yang@linux.dev> <20260914111940.f7e2c72eac4a2df97a646793@linux-foundation.org> Content-Language: en-US From: Lance Yang In-Reply-To: <20260914111940.f7e2c72eac4a2df97a646793@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 6CF601C0003 X-Stat-Signature: icgkgbkzo4twmyoe74ybqgq9mf9w741g X-Rspamd-Server: rspam01 X-HE-Tag: 1789479806-525570 X-HE-Meta: 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 tNM+y+Ne K36DEJwk1DL3YTLfgC3x/MqMivF/h0IzwG40fHBhi9eCL1hrV/ca4G83P1/YGtrwAdFdl6uLif4Ng4WKMrirrW8i4YHfcEPsMrQbYkBKfUH5CpT3LY12JuoU54NtTs1CTW3GoXhLCuwymiSpVCsJnI5doCKh0Ae35VI1OMZfyBFpUOZYo/2IyD6lSDLAgMyG5HtPzo0yv+OBgP00RRihlL2d8AyibKcK5C7pu+9jbu1YIxM7oUYVXVYGf6xHOdskb5str9z0A5LnULWaVPo/cmT91Q6oXnWUE0GAGAqO8Fzxi4w97eLdeU6XoeXbEGmQkev4vc93CajLUlAX3VI9q6EpE2UbSSscOgj5T Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/9/15 02:19, Andrew Morton wrote: > On Mon, 14 Sep 2026 16:29:00 +0200 "David Hildenbrand (Arm)" wrote: > >> On 9/14/26 12:59, Kiryl Shutsemau wrote: >>> On Sun, Sep 13, 2026 at 03:23:12PM +0800, Lance Yang wrote: >>>> >>>> On Sat, Sep 12, 2026 at 11:46:35PM -0700, Andrew Morton wrote: >>>>> >>>>> >>>>> That's the sort of thing we'd prefer to avoid. >>>>> >>>>> >>>>> How real is this? Is there a reported-by:? Do you have a reproducer? >>>> >>>> Yes, I reproduced it on x86 with a small test module. It sets >>>> VM_MIXEDMAP | VM_HUGEPAGE and calls vmf_insert_pfn_pmd() with >>>> huge_zero_pfn, without touching the page tables directly. A full-PMD >>>> munmap() crashes before the split series[1] as well. >>> >>> Ah. So there's no real bug upstream, right? >> >> Matches my understanding. > > Thanks. I'll remove cc:stable, move this into mm-unstable as a > next-merge-window thing. Sounds good to me, thanks, Andrew! Kiryl, David, would you prefer the validation for raw-PFN mappings of the huge zero page as a separate follow-up, or should that validation replace this patch? wdyt Cheers, Lance