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b=KdQrzR3vf+z1dXt8moVE4lWL0xR6YvwRPceeAI609o8bZcg0tfarInopUZdeROePM MzbHN7CuSrgHjf2d6E3N34UssO7AdaZLpXc8x8qV6la0CuoHkV7BzW0wYqy9vWsEnN zqrejZxeQWsmg03EZUrEmhytog3MWalbPNdPhzfB1sCQxBENXv1srgxqZQCWyq+gGd r/pL0Dvss93HZcQ0j/doy+dMk09NmRk76+wCr1wofTRm5EPDthGgzViu61q2QtSpms cbCmjww2cTrehhj0y7cvy1PYaAD88KbMJc1mMg61gXLcdtgzfpTs9XXtytuFksal/V U26qPyjAo2dzQ== Message-ID: <7b78c1d8-9efc-4570-8f4c-244af665a159@kernel.org> Date: Wed, 12 Nov 2025 09:05:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: fix handling of zero page in follow_page_pte() To: peng8420.li@gmail.com, linux-mm@kvack.org, akpm@linux-foundation.org Cc: osalvador@suse.de, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, linux-kernel@vger.kernel.org, dan.j.williams@intel.com References: <20251112072424.125514-1-peng8420.li@gmail.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251112072424.125514-1-peng8420.li@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 70DBDC0011 X-Stat-Signature: utme7tm81syeej768jetcoancdx7zocx X-HE-Tag: 1762934712-44227 X-HE-Meta: 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 BusnNE2U ObRCe2Tq4CcaZA+moK6PSxOgYWhgNEECqmbBwZ4zXIjLeyd5fPejXr2qY0L1mZPVbrK9z2ej1Gjuy0sQqRzsRaBbC0yYjpQjEvcjsoAaWauR60MIHfGZKDfpqLyeGWmIFjp0D3yRyOBFFkAwh1UewUstYVtMigfAHI86rkYU6V2tKGPpT7YUCljI3r+WX59ln0ryWtx14bSE20XHXPhSqEehX9lnq2uVGsN2J9g4xogOq7ss65dZXrtvD01woA8Qcw/iwx9U8hdvos2uolQZ6QTwBMEF5ZKrPlkt5aQVonupCQoGbYJB/hFaBZ9n9D35NKGpEvuk5MoWOK9b6ymKbHpozhYhuYTPAgs1VYRsw56nArkDuj3elS1VEo9gXAW/+e5jBISpgANhZ6LE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12.11.25 08:24, peng8420.li@gmail.com wrote: > From: "peng8420.li" > > In some scenarios, `__vm_normal_page` might return NULL. > In this case, if `is_zero_pfn(pte_pfn(pte))` is true, simply return `page = pte_page(pte)`; > no further folio processing is needed. > > Signed-off-by: peng8420.li > --- > mm/gup.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/gup.c b/mm/gup.c > index 95d948c8e86c..60ae5f0c20e0 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -838,6 +838,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, > > if (is_zero_pfn(pte_pfn(pte))) { > page = pte_page(pte); > + goto out; > } else { > ret = follow_pfn_pte(vma, address, ptep, flags); > page = ERR_PTR(ret); I'm sorry, but that's just wrong. Observe how me might run into the gup_must_unshare() branch and how try_grab_folio() would grab references on the FOLL_GET path. -- Cheers David