From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f200.google.com (mail-pf1-f200.google.com [209.85.210.200]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F7754749D5 for ; Tue, 4 Aug 2026 18:51:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.200 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785869475; cv=none; b=aO+E5kvmvQhwoosZi4GsMLrbC0ubYLhoxTK4kuXp1Q+Pc76fNOeFlgRmicW/lvYtcw4QJLUPyKcA1ywE9E9+8jZ3SEy7N2mvuyhV9kWbSBNFQKmN1kVPrx+uk2h3ynd/FuqhDg/QhC4tzIDU5D48oCXIYqajV8XWCvut9WOiPOo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785869475; c=relaxed/simple; bh=/pi0kNXNY1h1pfxpiwUj6T06M1fqxSotc6q0idZPb1E=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=obQ04q+/ENQDIdsSPhG8iWOR1HoW1Go1ZXW1WPMHdBjXNRNmv0xiJrXYElWJk7O7zpSrUDtAkY/ZlyxdI+lvgHuYbblpC9A0cB8WdBveYpYFrLA09uLwNNkkHT8/3FTs//VLSgPt+A/OMI0Qk52yxc7fWKNKn8lT5p27a8BGI90= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--praan.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=r7NToLc2; arc=none smtp.client-ip=209.85.210.200 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--praan.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="r7NToLc2" Received: by mail-pf1-f200.google.com with SMTP id d2e1a72fcca58-84e048a801dso152748b3a.3 for ; Tue, 04 Aug 2026 11:51:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785869473; x=1786474273; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=6S00Ge/ZDy4xJEvv5eN0PZrlFX4UFgt2/k8ihNKAOGs=; b=r7NToLc206L8dkkIq/zyZt4LEG/oj1/vjEU+dV2kdHLgIViXtVxjBXt4utVsjYPnkg GxOahNhBqnXoK1qG7AjVt25/deKwt3kNftL44X81bN/C9aQGHTsjdJafvs6aS6WQtkYW 9okE9Vti/5ca7kCR7NnUSWbbpQEDOq8T0/Iucgmbr4kIyP+6fEq0hZw9hXFMbFvh+MBc ms42DINkwgPbSLdodwpJZobm5JVcwbDE/9j7tGiq+AkFtVURqzG5cHMARe+FX+GJCTeF KXX2L0muy/dvchat20y512DiOXDm6sgHN46yTxQeNrfxNnwPNf1KAeIK5cXAJBfG1oHN o7cg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785869473; x=1786474273; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=6S00Ge/ZDy4xJEvv5eN0PZrlFX4UFgt2/k8ihNKAOGs=; b=HWzIbaXEV2TkBtnz+DCSooEkBWSbtkkeZV2n7SF8yQvwQp5jNByeGjjyMx92AyaMDp sVnEAfjONkeF/NoRunCDzu5yYaeyUpnFm9j1jecARJaoiz6MSUmk11gnUeI8+kUayhHp /3la8VzsRVvTa5wYXBYH8C8WlhxjMui/xZPcPsjdsTLOXltEhkFo4P59lJlS+V/bWWEl XJ0l9xRsezEnz22LW32ZajTvTBZrlaF54Nn1eKENg9jPc2K1fr5ZxY1U31iQbFhFhkEA Gun0bKUrVizhu3hWkLCDj3gWIYVuIFsiq1D0ne8dKzygd+7COhCWIP0qQiCtiSaJnnm4 rWEw== X-Forwarded-Encrypted: i=1; AHgh+RoWKUKY0pnogfe+9KMpIXUp7J/BA0XC9Z8jcjlbZ1lyCswV/atDwWLBY/+SFd49Q8lsYtVebML/r1NNSro=@vger.kernel.org X-Gm-Message-State: AOJu0Yx0rAyYT/xIynw5iForaKHSwdyMNPX+KFvWpihSXla7nqD5gfIH i5CCktk8jKFF+7w3B0/I2nUQtPfpBBOBbf2hvNxiqtHVhSDgqj+WGbYmY2S4cUfRSjUAGZ4XTTo Z+w== X-Received: from pgvm5.prod.google.com ([2002:a65:62c5:0:b0:cb5:3dd0:cdbd]) (user=praan job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:348d:b0:842:706e:ad43 with SMTP id d2e1a72fcca58-84f2e0ccba3mr802967b3a.33.1785869472550; Tue, 04 Aug 2026 11:51:12 -0700 (PDT) Date: Tue, 4 Aug 2026 18:50:48 +0000 In-Reply-To: <20260804185050.2053672-1-praan@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260804185050.2053672-1-praan@google.com> X-Mailer: git-send-email 2.55.0.571.g244d577d93-goog Message-ID: <20260804185050.2053672-4-praan@google.com> Subject: [RFC PATCH v2 3/5] vfio/pci: Implement page-backed .map_dma_buf handler From: Pranjal Shrivastava To: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Bjorn Helgaas , Logan Gunthorpe , Alex Williamson , Jason Gunthorpe , Kevin Tian , Pranjal Shrivastava , Ankit Agrawal , Matt Evans , Vivek Kasireddy , Leon Romanovsky , Shivaji Kant , Samiullah Khawaja , Unnati Sachan Content-Type: text/plain; charset="UTF-8" When a DMABUF is backed by ZONE_DEVICE pages, the standard raw PFN scatterlist builder (dma_buf_phys_vec_to_sgt) cannot be used because it explicitly drops page metadata pointers. Implement a map_dma_buf helper that loops through existing contiguous physical ranges and generates SGL entries directly via sg_set_page while maps using the standard dma_map_sgtable. Implement a corresponding .unmap_dma_buf as well. Signed-off-by: Pranjal Shrivastava --- drivers/vfio/pci/vfio_pci_dmabuf.c | 81 ++++++++++++++++++++++++++++-- 1 file changed, 77 insertions(+), 4 deletions(-) diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c index 900ac1851c9f..b936da3bcada 100644 --- a/drivers/vfio/pci/vfio_pci_dmabuf.c +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c @@ -55,6 +55,7 @@ static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct * /* See comments in vfio_pci_core_mmap() re VM_ALLOW_ANY_UNCACHED. */ vm_flags_set(vma, VM_ALLOW_ANY_UNCACHED | VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); + vma->vm_private_data = priv; vfio_pci_set_vma_ops(vma); @@ -70,6 +71,66 @@ static void vfio_pci_dma_buf_done(struct kref *kref) complete(&priv->comp); } +/* + * For ZONE_DEVICE-backed DMABUFs, populate the scatterlist with struct page + * pointers so that dma_map_sgtable() can detect MEMORY_DEVICE_PCI_P2PDMA and + * perform peer-to-peer DMA mappings for importing devices. + */ +static struct sg_table * +vfio_pci_dma_buf_map_page_backed(struct dma_buf_attachment *attachment, + enum dma_data_direction dir) +{ + struct vfio_pci_dma_buf *priv = attachment->dmabuf->priv; + struct sg_table *sgt; + struct scatterlist *sgl; + unsigned int nents = 0; + int i, ret; + + for (i = 0; i < priv->nr_ranges; i++) { + unsigned int added = DIV_ROUND_UP(priv->phys_vec[i].len, + (UINT_MAX & PAGE_MASK)); + + if (check_add_overflow(nents, added, &nents)) + return ERR_PTR(-EOVERFLOW); + } + + sgt = kzalloc(sizeof(*sgt), GFP_KERNEL); + if (!sgt) + return ERR_PTR(-ENOMEM); + + ret = sg_alloc_table(sgt, nents, GFP_KERNEL); + if (ret) { + kfree(sgt); + return ERR_PTR(ret); + } + + sgl = sgt->sgl; + for (i = 0; i < priv->nr_ranges; i++) { + size_t range_len = priv->phys_vec[i].len; + unsigned long pfn = priv->phys_vec[i].paddr >> PAGE_SHIFT; + + while (range_len > 0) { + unsigned int chunk_len = min_t(size_t, range_len, (UINT_MAX & PAGE_MASK)); + struct page *page = pfn_to_page(pfn); + + sg_set_page(sgl, page, chunk_len, 0); + sgl = sg_next(sgl); + + range_len -= chunk_len; + pfn += chunk_len >> PAGE_SHIFT; + } + } + + ret = dma_map_sgtable(attachment->dev, sgt, dir, 0); + if (ret) { + sg_free_table(sgt); + kfree(sgt); + return ERR_PTR(ret); + } + + return sgt; +} + static struct sg_table * vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment, enum dma_data_direction dir) @@ -82,9 +143,14 @@ vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment, if (priv->status != VFIO_PCI_DMABUF_OK) return ERR_PTR(-ENODEV); - ret = dma_buf_phys_vec_to_sgt(attachment, priv->provider, - priv->phys_vec, priv->nr_ranges, - priv->size, dir); + if (priv->zone_device_backed) { + ret = vfio_pci_dma_buf_map_page_backed(attachment, dir); + } else { + ret = dma_buf_phys_vec_to_sgt(attachment, priv->provider, + priv->phys_vec, priv->nr_ranges, + priv->size, dir); + } + if (IS_ERR(ret)) return ret; @@ -100,7 +166,14 @@ static void vfio_pci_dma_buf_unmap(struct dma_buf_attachment *attachment, dma_resv_assert_held(priv->dmabuf->resv); - dma_buf_free_sgt(attachment, sgt, dir); + if (priv->zone_device_backed) { + dma_unmap_sgtable(attachment->dev, sgt, dir, 0); + sg_free_table(sgt); + kfree(sgt); + } else { + dma_buf_free_sgt(attachment, sgt, dir); + } + kref_put(&priv->kref, vfio_pci_dma_buf_done); } -- 2.55.0.571.g244d577d93-goog