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[80.230.48.7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-454917d57aesm35649963f8f.26.2026.05.12.14.07.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 May 2026 14:07:30 -0700 (PDT) Date: Tue, 12 May 2026 17:07:25 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Muchun Song , Oscar Salvador , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli Subject: [PATCH v7 26/31] virtio_balloon: skip zeroing for host-zeroed reported pages Message-ID: <73b896d7fc1b4bb6127f234f5e1964d2764cbf9a.1778616612.git.mst@redhat.com> References: MIME-Version: 1.0 In-Reply-To: X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 5nCp1aCzfLvboObtwh_TdN6ljutNhpjibIr1sZEiTG4_1778620053 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 22B2E20007 X-Stat-Signature: tfiup3ok8jxbpnz4z8tx87g53ghqjm5o X-HE-Tag: 1778620055-276578 X-HE-Meta: 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 zkbKmXEQ n8IPso4HO3j3nrWsTPqbqGR1ygDrnQUtE2M9287MoAh3uUb9C/VZApcZADsJdp6rD8soht5h9dJJLk6S1KHRzVLcyDkN7axFQI3hD3RU74X8G1zOeB6qKUmC77F3HZsZQ8NkfqB7yaXTeanDbJNxXmRYWOK76S3zuKesmNsYduGB4pSA/rCUL+8NbpVNk9SKZ+ro4ishen0RmZoU/lj0+A//tFRYrGJybNTIwp03L9MZuyAuBzB6y2lxFuL+yTxPwZO41ngwv9w+Xw+5VS69opxGoLc5z0PhJBlqIjvy+LMuGucDGrE07bVJHPTw9bqK+vydnBVPeeqvhikR2m9atW4aqpPfp8okJaKsT/rksuAEFZQuKKHmiG9VdZ1dhndWZTcF+a6dKthlOiNVo+xUqJ6tMqSgOX2ZweZSHOV/rAQHnsT8F5sWiwllURcTSIPDyPvUdurjWFXXyxIALmi1FGgHReg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Implement VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED (per virtio spec proposal): when negotiated, the device initializes reported pages (zeros, or poison_val if PAGE_POISON). Check per-page used length returned by the device to determine which reported pages were zeroed. If used_len matches the page size, the device successfully initialized the page (e.g. via MADV_DONTNEED), and we set the corresponding zeroed_bitmap bit. Gate host_zeroes_pages on the feature bit and page content: when PAGE_POISON is negotiated with non-zero poison_val, the device fills with poison not zeros, so pages are not zeroed. Clear the feature in validate() if REPORTING is not present or if PAGE_POISON is active with non-zero poison_val. See the virtio spec change: https://github.com/oasis-tcs/virtio-spec/issues/244 Signed-off-by: Michael S. Tsirkin Assisted-by: Claude:claude-opus-4-6 Assisted-by: cursor-agent:GPT-5.4-xhigh --- drivers/virtio/virtio_balloon.c | 22 ++++++++++++++++++++-- include/uapi/linux/virtio_balloon.h | 1 + 2 files changed, 21 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index fc43d0d7bbbc..6586699396b7 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -204,6 +204,8 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i struct virtqueue *vq = vb->reporting_vq; unsigned int i, err = 0; + bitmap_zero(pr_dev_info->zeroed_bitmap, nents); + /* We should always be able to add these buffers to an empty queue. */ for (i = 0; i < nents; i++) { struct scatterlist one; @@ -223,10 +225,14 @@ static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_i /* When host has read buffer, this completes via balloon_ack */ for (i = 0; i < nents; i++) { - unsigned int unused; + struct scatterlist *entry; + unsigned int used_len; wait_event(vb->acked, - virtqueue_get_buf(vq, &unused)); + (entry = virtqueue_get_buf(vq, &used_len))); + if (used_len == entry->length) + set_bit(entry - sg, + pr_dev_info->zeroed_bitmap); } } @@ -1048,6 +1054,9 @@ static int virtballoon_probe(struct virtio_device *vdev) #endif vb->pr_dev_info.capacity = capacity; + vb->pr_dev_info.host_zeroes_pages = + virtio_has_feature(vdev, + VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED); err = page_reporting_register(&vb->pr_dev_info); if (err) goto out_unregister_oom; @@ -1173,6 +1182,14 @@ static int virtballoon_validate(struct virtio_device *vdev) else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); + if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_REPORTING)) + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED); + + /* Device fills with poison_val, not zeros; disable zeroed hint */ + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON) && + !want_init_on_free()) + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED); + __virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM); return 0; } @@ -1184,6 +1201,7 @@ static unsigned int features[] = { VIRTIO_BALLOON_F_FREE_PAGE_HINT, VIRTIO_BALLOON_F_PAGE_POISON, VIRTIO_BALLOON_F_REPORTING, + VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED, }; static struct virtio_driver virtio_balloon_driver = { diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h index ee35a372805d..13074631f300 100644 --- a/include/uapi/linux/virtio_balloon.h +++ b/include/uapi/linux/virtio_balloon.h @@ -37,6 +37,7 @@ #define VIRTIO_BALLOON_F_FREE_PAGE_HINT 3 /* VQ to report free pages */ #define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */ #define VIRTIO_BALLOON_F_REPORTING 5 /* Page reporting virtqueue */ +#define VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED 6 /* Device initializes reported pages */ /* Size of a PFN in the balloon interface. */ #define VIRTIO_BALLOON_PFN_SHIFT 12 -- MST