From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender4-op-o11.zoho.com (sender4-op-o11.zoho.com [136.143.188.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9C1B123E25B for ; Tue, 11 Aug 2026 15:50:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.11 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786463405; cv=pass; b=FA/e3T7XmeqRoWS/mvgRCz39QnMvUlkSC0v2g5krsDHsUvpeUtUeiEsuZUNvp9uzGdCQ74jRZNWBPRpbAuQ0Z9Dr6bKBh3SK+/QVTE1dFSjccg7FkBmasSLeMmMrBl5YVg1meUCxFZtA9K1faMMqAMCKbq1ykn8ruK7clqRHijk= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786463405; c=relaxed/simple; bh=CVVOR1DtQRfbI1f/+QElcrYREMqfgwytIXwI5VouXu8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jNyxwRgsfEi2Q9pZaGwJxEdAcwRbJF93G2OGxl5Hak2FNNYGHP+6/o/BPpFaJgYbqvwoEaMuunZR9NBvsCEm5CKeDzxG9BNW8sK+8IMLAMp3R5mziQRNHxS3SNIA+NNTPJHKP0izOT25yCMDEdqfZqtJpvCOK/UcRH8dIYws6Rk= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (1024-bit key) header.d=collabora.com header.i=dmitry.osipenko@collabora.com header.b=Lq/b1qSs; arc=pass smtp.client-ip=136.143.188.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=collabora.com header.i=dmitry.osipenko@collabora.com header.b="Lq/b1qSs" ARC-Seal: i=1; a=rsa-sha256; t=1786463371; cv=none; d=zohomail.com; s=zohoarc; b=IPbOA7iqYU4NZ+6LG31zWs11yB242BhxW7HJqDty6P6eky+C7Yrsz+pe9iIkk3QT4bqWAuUiFrAwT8BRXeHbKxNFlNmPnqb3NDIuEcB9LK/0p5wQJbUGhq8MKG+c7nvK2A2SmWha5akxrcvJ81XT4NAJXV39QG888Z/fl4NyMXU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1786463371; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:Subject:Subject:To:To:Message-Id:Reply-To; bh=wJ+mE/6pcm4lW/l9xvOfruk8A2xPzxyqDey8hIf/l5U=; b=AMCSv6Io8pKITmE2viU0V7/4Bd1w0bGz2GsRXid+8ChOqS0DDlHX0nE9LWU28lgY0Rr+6muznjNb/0SkJKxMQhNeOuVcQK1atX5cYayqQxOMwfMQfhVT5VdYsSZZmV8TcGqkXdbKLNEkF5ctS+Oka95s7wzwkBbzWIIVcWEshaA= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=dmitry.osipenko@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1786463371; s=zohomail; d=collabora.com; i=dmitry.osipenko@collabora.com; h=Message-ID:Date:Date:MIME-Version:Subject:Subject:To:To:Cc:Cc:From:From:In-Reply-To:Content-Type:Content-Transfer-Encoding:Message-Id:Reply-To; bh=wJ+mE/6pcm4lW/l9xvOfruk8A2xPzxyqDey8hIf/l5U=; b=Lq/b1qSsRAoPEXX7g9mx3mFNbcho/oNs7UuxztajAgkQXCbZG++IWLuGo3H6Brer NPUa9D5LtvJm9aZujJq1QPdJc2hEvwv+/vn2726FPKEN4+oft163blIxp/gjAZcdtMM Gg87rgJh21tZvWIAc9eSuz3MC1RxNdUbwYkiz6CM= Received: by mx.zohomail.com with SMTPS id 1786463370473304.88449999785416; Tue, 11 Aug 2026 08:49:30 -0700 (PDT) Message-ID: Date: Tue, 11 Aug 2026 18:49:25 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/virtio: use the DMA API for resource backing on Xen To: benjamin@edera.io, David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Simona Vetter Cc: dri-devel@lists.freedesktop.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260806-virtgpu-xen-dma-v1-1-e499b345bbad@edera.io> Content-Language: en-US From: Dmitry Osipenko In-Reply-To: <20260806-virtgpu-xen-dma-v1-1-e499b345bbad@edera.io> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ZohoMailClient: External On 8/7/26 01:54, Benjamin Leggett via B4 Relay wrote: > From: Benjamin Leggett > > On a Xen PV domain page addresses bear no relation to the real machine > addresses the host would have to use to reach it. > virtio_ring.c handles this correctly, vring_use_map_api() returns true > for any xen_domain() regardless of VIRTIO_F_ACCESS_PLATFORM. > > virtio-gpu makes the same decision independently, but its copy > looks only at the feature bit: > > bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > > QEMU does not set iommu_platform on virtio-vga by default, so > VIRTIO_F_ACCESS_PLATFORM is not negotiated, use_dma_api is false, and > virtio_gpu_object_shmem_init() describes the framebuffer's backing pages > to the host with sg_phys(). Those are guest-physical addresses. In a PV > domain they resolve, on the host side, to pages belonging to some other > domain, so the host scans out unrelated memory. > > Move the decision into virtio_gpu_use_dma_api() and give it the > xen_domain() check, like vring_use_map_api() has. This > additionally enables the dma_sync_sgtable_for_device() calls in > virtgpu_vq.c, which are required for correctness whenever swiotlb > is in play. > > Reproduced with a Xen 4.21 PV dom0 nested inside QEMU 8.2 with > virtio-vga, on both a distro 6.8 kernel and 6.18 LTS. A PVH dom0 > works fine and doesn't need this fix because it is identity-mapped, > only PV dom0s are affected. > > Fixes: a3b815f09bb8 ("drm/virtio: add iommu support.") > Signed-off-by: Ben Leggett > --- > drivers/gpu/drm/virtio/virtgpu_drv.h | 20 ++++++++++++++++++++ > drivers/gpu/drm/virtio/virtgpu_object.c | 2 +- > drivers/gpu/drm/virtio/virtgpu_vq.c | 6 +++--- > 3 files changed, 24 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h > index 17a6a4d26516..09da7973387e 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_drv.h > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h > @@ -43,6 +43,8 @@ > #include > #include > > +#include > + > #define DRIVER_NAME "virtio_gpu" > #define DRIVER_DESC "virtio GPU" > > @@ -60,6 +62,24 @@ > /* See virtio_gpu_ctx_create. One additional character for NULL terminator. */ > #define DEBUG_NAME_MAX_LEN 65 > > +/* > + * Whether the host must be told about resource backing pages by DMA address > + * rather than guest-physical address. > + * > + * This mirrors vring_use_map_api() in drivers/virtio/virtio_ring.c, including > + * its xen_domain() case. > + */ > +static inline bool virtio_gpu_use_dma_api(const struct virtio_device *vdev) > +{ > + if (!virtio_has_dma_quirk(vdev)) > + return true; > + > + if (xen_domain()) > + return true; > + > + return false; > +} > + > struct virtio_gpu_object_params { > unsigned long size; > bool dumb; > diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c > index 9bc0bd68c314..49899485be6f 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_object.c > +++ b/drivers/gpu/drm/virtio/virtgpu_object.c > @@ -173,7 +173,7 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev, > struct virtio_gpu_mem_entry **ents, > unsigned int *nents) > { > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > struct scatterlist *sg; > struct sg_table *pages; > int si; > diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c > index 905b1f42cd98..568fefd713e0 100644 > --- a/drivers/gpu/drm/virtio/virtgpu_vq.c > +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c > @@ -764,7 +764,7 @@ int virtio_gpu_panic_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev, > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]); > struct virtio_gpu_transfer_to_host_2d *cmd_p; > struct virtio_gpu_vbuffer *vbuf; > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > > if (virtio_gpu_is_shmem(bo) && use_dma_api) > dma_sync_sgtable_for_device(vgdev->vdev->dev.parent, > @@ -795,7 +795,7 @@ void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev, > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]); > struct virtio_gpu_transfer_to_host_2d *cmd_p; > struct virtio_gpu_vbuffer *vbuf; > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > > if (virtio_gpu_is_shmem(bo) && use_dma_api) > dma_sync_sgtable_for_device(vgdev->vdev->dev.parent, > @@ -1231,7 +1231,7 @@ void virtio_gpu_cmd_transfer_to_host_3d(struct virtio_gpu_device *vgdev, > struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(objs->objs[0]); > struct virtio_gpu_transfer_host_3d *cmd_p; > struct virtio_gpu_vbuffer *vbuf; > - bool use_dma_api = !virtio_has_dma_quirk(vgdev->vdev); > + bool use_dma_api = virtio_gpu_use_dma_api(vgdev->vdev); > > if (virtio_gpu_is_shmem(bo) && use_dma_api) > dma_sync_sgtable_for_device(vgdev->vdev->dev.parent, > > --- > base-commit: bd4f284df04d76fd65e57141cb1e6e7a49e4c3cb > change-id: 20260806-virtgpu-xen-dma-559fab712250 > > Best regards, Looks okay, though I'm not familiar with Xen. Will apply to -next in a day if nobody will have objections. Acked-by: Dmitry Osipenko -- Best regards, Dmitry