linux-kernel - [PATCH] xen/virtio: Don't use grant-dma-ops when running as Dom0

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Message-Id: <6698564dd2270a9f7377b78ebfb20cb425cabbe8.1767720955.git.teddy.astie@vates.tech>
Date: Tue, 06 Jan 2026 17:36:50 +0000
From: "Teddy Astie" <teddy.astie@...es.tech>
To: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc: "Teddy Astie" <teddy.astie@...es.tech>, "Juergen Gross" <jgross@...e.com>, "Stefano Stabellini" <sstabellini@...nel.org>, "Oleksandr Tyshchenko" <oleksandr_tyshchenko@...m.com>, "Boris Ostrovsky" <boris.ostrovsky@...cle.com>
Subject: [PATCH] xen/virtio: Don't use grant-dma-ops when running as Dom0

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@...es.tech>
Fixes: 61367688f1fb0 ("xen/virtio: enable grant based virtio on x86")
---
CC: Juergen Gross <jgross@...e.com>
CC: Stefano Stabellini <sstabellini@...nel.org>
CC: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
CC: Boris Ostrovsky <boris.ostrovsky@...cle.com>

 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;
-- 
2.52.0



--
Teddy Astie | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech