On Tue, Feb 03, 2026 at 06:59:35PM +0000, Robin Murphy wrote:

On 2026-02-03 5:55 pm, Jason Gunthorpe wrote:

quoted

On Tue, Feb 03, 2026 at 09:45:17AM -0800, Nicolin Chen wrote:

quoted

Btw, attaching to IOMMU_DOMAIN_BLOCKED/group->blocking_domain is not
allowed in general if require_direct=true. I assume this case can be
an exception since there's no point in allowing a device that has no
driver yet to access any reserved region?

No, the point of RMRs in general is that the device can be assumed to
already be accessing them, and that access must be preserved, regardless of
whether an OS driver may or may not take over the device later.

I see. Thanks for the input.

In fact RMRs
with the "Remapping Permitted" flag are only strictly needed *until* an OS
driver has taken control over whatever it was that firmware left them doing.

Yes. I see that doesn't set require_direct.

Nicolin