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Tsirkin" , Jason Wang , Mike Christie , Paolo Bonzini , Stefan Hajnoczi , =?UTF-8?q?Eugenio=20P=C3=A9rez?= , virtualization@lists.linux.dev, kvm@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Karthikeyan KS , John Hubbard Subject: [PATCH] vhost-scsi: use FOLL_PIN for DMA page pinning Date: Wed, 7 Oct 2026 16:37:16 +0000 Message-ID: <20261007163716.707102-1-karthiproffesional@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vhost_scsi_map_to_sgl() pins guest buffer pages via iov_iter_get_pages2() (FOLL_GET), which does not prevent copy-on-write or page migration while DMA is in flight. Switch to iov_iter_extract_pages() (FOLL_PIN), which does. Cc: Jason Wang Cc: Mike Christie Cc: John Hubbard Cc: Michael S. Tsirkin Cc: virtualization@lists.linux.dev Signed-off-by: Karthikeyan KS --- drivers/vhost/scsi.c | 49 ++++++++++++++++++++++++++++++-------------- 1 file changed, 34 insertions(+), 15 deletions(-) diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c index 7a1f39a327da..e14b4da4ea9c 100644 --- a/drivers/vhost/scsi.c +++ b/drivers/vhost/scsi.c @@ -115,6 +115,8 @@ struct vhost_scsi_cmd { u32 tvc_sgl_count; u32 tvc_prot_sgl_count; u32 copied_iov:1; + u32 tvc_need_unpin:1; + u32 tvc_prot_need_unpin:1; const void *read_iov; struct iov_iter *read_iter; struct scatterlist *sgl; @@ -433,8 +435,13 @@ static void vhost_scsi_release_cmd_res(struct se_cmd *se_cmd) if (tv_cmd->copied_iov) __free_page(page); - else - put_page(page); + else if (tv_cmd->tvc_need_unpin) + unpin_user_page(page); + /* + * Else: iov_iter_extract_pages() took neither a ref + * nor a pin on this page (ITER_KVEC/BVEC/etc), so + * there is nothing to release here. + */ } kfree(tv_cmd->read_iter); kfree(tv_cmd->read_iov); @@ -443,8 +450,8 @@ static void vhost_scsi_release_cmd_res(struct se_cmd *se_cmd) if (tv_cmd->tvc_prot_sgl_count) { for_each_sgtable_sg(&tv_cmd->prot_table, sg, i) { page = sg_page(sg); - if (page) - put_page(page); + if (page && tv_cmd->tvc_prot_need_unpin) + unpin_user_page(page); } sg_free_table_chained(&tv_cmd->prot_table, vs->inline_sg_cnt); } @@ -773,7 +780,8 @@ vhost_scsi_get_cmd(struct vhost_virtqueue *vq, u64 scsi_tag) static void vhost_scsi_revert_map_iov_to_sgl(struct iov_iter *iter, struct scatterlist *curr, - struct scatterlist *end) + struct scatterlist *end, + bool need_unpin) { size_t revert_bytes = 0; struct page *page; @@ -782,7 +790,8 @@ static void vhost_scsi_revert_map_iov_to_sgl(struct iov_iter *iter, page = sg_page(curr); if (page) { - put_page(page); + if (need_unpin) + unpin_user_page(page); revert_bytes += curr->length; } /* Clear so we can re-use it for the copy path */ @@ -812,9 +821,9 @@ vhost_scsi_map_to_sgl(struct vhost_scsi_cmd *cmd, size_t offset; unsigned int n, npages = 0; - bytes = iov_iter_get_pages2(iter, pages, LONG_MAX, - VHOST_SCSI_PREALLOC_UPAGES, &offset); - /* No pages were pinned */ + bytes = iov_iter_extract_pages(iter, &pages, LONG_MAX, + VHOST_SCSI_PREALLOC_UPAGES, 0, &offset); + /* No pages were extracted */ if (bytes <= 0) return bytes < 0 ? bytes : -EFAULT; @@ -837,7 +846,7 @@ vhost_scsi_map_to_sgl(struct vhost_scsi_cmd *cmd, cmd->tvc_sgl_count > BIO_MAX_VECS) { WARN_ONCE(true, "vhost-scsi detected misaligned IO. Performance may be degraded."); - goto revert_iter_get_pages; + goto revert_iter_extract_pages; } sg_set_page(sg, pages[npages++], n, offset); @@ -849,14 +858,17 @@ vhost_scsi_map_to_sgl(struct vhost_scsi_cmd *cmd, *sgl = sg; return npages; -revert_iter_get_pages: - vhost_scsi_revert_map_iov_to_sgl(iter, *sgl, sg); +revert_iter_extract_pages: + vhost_scsi_revert_map_iov_to_sgl(iter, *sgl, sg, + is_prot ? cmd->tvc_prot_need_unpin : cmd->tvc_need_unpin); iov_iter_revert(iter, bytes); while (bytes) { n = min_t(unsigned int, PAGE_SIZE, bytes); - put_page(pages[npages++]); + if (is_prot ? cmd->tvc_prot_need_unpin : cmd->tvc_need_unpin) + unpin_user_page(pages[npages]); + npages++; bytes -= n; } @@ -926,6 +938,7 @@ vhost_scsi_copy_iov_to_sgl(struct vhost_scsi_cmd *cmd, struct iov_iter *iter, } cmd->copied_iov = 1; + cmd->tvc_need_unpin = 0; return 0; err: @@ -950,11 +963,17 @@ vhost_scsi_map_iov_to_sgl(struct vhost_scsi_cmd *cmd, struct iov_iter *iter, struct scatterlist *sg = sg_table->sgl; int ret; + if (is_prot) + cmd->tvc_prot_need_unpin = iov_iter_extract_will_pin(iter); + else + cmd->tvc_need_unpin = iov_iter_extract_will_pin(iter); + while (iov_iter_count(iter)) { ret = vhost_scsi_map_to_sgl(cmd, iter, sg_table, &sg, is_prot); if (ret < 0) { vhost_scsi_revert_map_iov_to_sgl(iter, sg_table->sgl, - sg); + sg, is_prot ? cmd->tvc_prot_need_unpin : + cmd->tvc_need_unpin); return ret; } } @@ -1392,7 +1411,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq) /* * If T10_PI header + payload is present, setup prot_iter values * and recalculate data_iter for vhost_scsi_mapal() mapping to - * host scatterlists via get_user_pages_fast(). + * host scatterlists via iov_iter_extract_pages(). */ if (t10_pi) { if (v_req_pi.pi_bytesout) { -- 2.43.0