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Re: [PATCH] xen/virtio: Don't use grant-dma-ops when running as Dom0
- To: Teddy Astie <teddy.astie@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
- From: Jürgen Groß <jgross@xxxxxxxx>
- Date: Tue, 6 Jan 2026 20:03:39 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Delivery-date: Tue, 06 Jan 2026 19:03:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06.01.26 18:36, Teddy Astie wrote:
Dom0 inherit devices from the machine and is usually in PV mode.
If we are running in a virtual that has virtio devices, these devices
would be considered as using grants with Dom0 as backend, while being
the said Dom0 itself, while we want to use these devices like regular
PCI devices.
Fix this by preventing grant-dma-ops from being used when running as Dom0
(initial domain). We still keep the device-tree logic as-is.
Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
Fixes: 61367688f1fb0 ("xen/virtio: enable grant based virtio on x86")
---
CC: Juergen Gross <jgross@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
drivers/xen/grant-dma-ops.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index 14077d23f2a1..c2603e700178 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -366,7 +366,8 @@ static int xen_grant_init_backend_domid(struct device *dev,
if (np) {
ret = xen_dt_grant_init_backend_domid(dev, np, backend_domid);
of_node_put(np);
- } else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) ||
xen_pv_domain()) {
+ } else if (!xen_initial_domain() &&
+ (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) ||
xen_pv_domain())) {
dev_info(dev, "Using dom0 as backend\n");
*backend_domid = 0;
ret = 0;
Please make this controllable, e.g. via a boot parameter.
It is completely valid to have a virtio device in dom0 with the backend in
a domU. You'll need grants in this case.
Juergen
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