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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <0b168d85-443c-4f38-92f8-8c008b2f8b82@vates.tech>
Date: Tue, 06 Jan 2026 22:47:19 +0000
From: "Teddy Astie" <teddy.astie@...es.tech>
To: "Jürgen Groß" <jgross@...e.com>, xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc: "Stefano Stabellini" <sstabellini@...nel.org>, "Oleksandr Tyshchenko" <oleksandr_tyshchenko@...m.com>, "Boris Ostrovsky" <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH] xen/virtio: Don't use grant-dma-ops when running as Dom0

Le 06/01/2026 à 20:06, Jürgen Groß a écrit :
> 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@...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;
> 
> 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.
> 
Due to
 > *backend_domid = 0

Dom0 would always be the backend, unless we introduce a new boot 
parameter to select which domain will be the backend.

There is also another issue, as in the xen_initial_domain() case, all 
PCI devices come from hardware. So no virtio-pci device can't come from 
another domain as Linux would pick up pcifront devices only if we are 
not a Dom0 (!xen_initial_domain()).

> 
> Juergen

Teddy


--
Teddy Astie | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech