linux-kernel - RE: [PATCH v2 08/22] iommufd: Abstract iopt_pin_pages and iopt_unpin

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Message-ID: <BN9PR11MB52762F5A464ACC68D78465578C892@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 6 May 2025 09:36:38 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>, "jgg@...dia.com" <jgg@...dia.com>,
	"corbet@....net" <corbet@....net>, "will@...nel.org" <will@...nel.org>
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Subject: RE: [PATCH v2 08/22] iommufd: Abstract iopt_pin_pages and
 iopt_unpin_pages helpers

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Saturday, April 26, 2025 1:58 PM
> 
> The new vCMDQ object will be added for HW to access the guest memory for
> a
> HW-accelerated virtualization feature. It needs to ensure the guest memory
> pages are pinned when HW accesses them and they are contiguous in
> physical
> address space.
> 
> This is very like the existing iommufd_access_pin_pages() that outputs the
> pinned page list for the caller to test its contiguity.
> 
> Move those code from iommufd_access_pin/unpin_pages() and related
> function
> for a pair of iopt helpers that can be shared with the vCMDQ allocator. As
> the vCMDQ allocator will be a user-space triggered ioctl function, WARN_ON
> would not be a good fit in the new iopt_unpin_pages(), thus change them to
> use WARN_ON_ONCE instead.
> 
> Rename check_area_prot() to align with the existing iopt_area helpers, and
> inline it to the header since iommufd_access_rw() still uses it.
> 
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>

any reason why this cannot be done by the core? all types of vcmd
queues need to pin the guest buffer pages, no matter the IOMMU
accesses GPA or HPA.

Jason made a similar comment earlier [1]. 

check of continuity is still done by the driver, if HPA is being accessed.

[1] https://lore.kernel.org/all/20250424134049.GP1648741@nvidia.com/