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Re: [PATCH 07/20] xen/arm: vIOMMU: Add cmdline boot option "viommu = <boolean>"
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Milan Djokic <milan_djokic@xxxxxxxx>
- Date: Wed, 13 Aug 2025 12:30:48 +0200
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- Cc: Rahul Singh <rahul.singh@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 13 Aug 2025 10:31:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Hello Jan,
On 8/8/25 08:20, Jan Beulich wrote:
On 07.08.2025 18:59, Milan Djokic wrote:
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2058,6 +2058,13 @@ This option can be specified more than once (up to 8
times at present).
Flag to enable or disable support for PCI passthrough
+### viommu (arm)
+> `= <boolean>`
+
+> Default: `false`
+
+Flag to enable or disable support for Virtual IOMMU for guests.
Isn't this too coarse-grained? IOW don't you want to specify the kind of IOMMU
to use, even if right now only one is being implemented? Also - why on the
command line? Isn't this rather a per-guest setting?
Yes, it would make more sense to specify IOMMU kind instead of plain
enable/disable parameter. Updated in new patch series version.
As for reasons to have this parameter in xen command line, it is needed
for xen smmuv3 driver initialization, where viommu initialization is
done if 'viommu' is enabled. Also, for dom0less mode and dom0 itself,
viommu for domain is enabled while domain is created based on this
argument. We do have per-guest viommu enablement option for guests
created with xl, but this does not cover dom0 (and dom0-less).
### pcid (x86)
> `= <boolean> | xpti=<bool>`
Also, seeing this adjacent entry, you're inserting in the wrong place. The
options are supposed to be alphabetically sorted.
We'll fix this in the new version with other suggested changes included.
Jan
BR,
Milan
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