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Tue, 21 Apr 2026 18:17:58 -0700 (PDT) Received: from [192.168.1.150] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7dce20ff8c3sm1731771a34.22.2026.04.21.18.17.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Apr 2026 18:17:57 -0700 (PDT) Message-ID: Date: Tue, 21 Apr 2026 19:17:57 -0600 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] io_uring: take page references for NOMMU pbuf_ring mmaps From: Jens Axboe To: io-uring@vger.kernel.org, Greg Kroah-Hartman References: <2026042115-body-attention-d15b@gregkh> <177679318887.642042.703437019420919449.b4-ty@b4> Content-Language: en-US In-Reply-To: <177679318887.642042.703437019420919449.b4-ty@b4> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/21/26 11:39 AM, Jens Axboe wrote: > > On Tue, 21 Apr 2026 15:46:16 +0200, Greg Kroah-Hartman wrote: >> Under !CONFIG_MMU, io_uring_get_unmapped_area() returns the kernel >> virtual address of the io_mapped_region's backing pages directly; >> the user's VMA aliases the kernel allocation. io_uring_mmap() then >> just returns 0 -- it takes no page references. >> >> The CONFIG_MMU path uses vm_insert_pages(), which takes a reference on >> each inserted page. Those references are released when the VMA is torn >> down (zap_pte_range -> put_page). io_free_region() -> release_pages() >> drops the io_uring-side references, but the pages survive until munmap >> drops the VMA-side references. >> >> [...] > > Applied, thanks! > > [1/1] io_uring: take page references for NOMMU pbuf_ring mmaps > commit: d9b7b3d9c5286a786c7fe8220c55a6e012088c2e Actually, I take that back - what prevents the io_mmap_get_region() in the newly added io_uring_nommu_vm_close() from getting the same region that we initially referenced the pages from in the nommu variant of io_uring_mmap()? -- Jens Axboe