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

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Message-ID: <376566b4-6c13-45ad-b1e5-8cfe2de437bc@linux.intel.com>
Date: Sun, 27 Apr 2025 15:22:13 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Nicolin Chen <nicolinc@...dia.com>, jgg@...dia.com, kevin.tian@...el.com,
 corbet@....net, will@...nel.org
Cc: bagasdotme@...il.com, robin.murphy@....com, joro@...tes.org,
 thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
 shuah@...nel.org, jsnitsel@...hat.com, nathan@...nel.org,
 peterz@...radead.org, yi.l.liu@...el.com, mshavit@...gle.com,
 praan@...gle.com, zhangzekun11@...wei.com, iommu@...ts.linux.dev,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
 linux-kselftest@...r.kernel.org, patches@...ts.linux.dev, mochs@...dia.com,
 alok.a.tiwari@...cle.com, vasant.hegde@....com
Subject: Re: [PATCH v2 08/22] iommufd: Abstract iopt_pin_pages and
 iopt_unpin_pages helpers

On 4/26/25 13:58, Nicolin Chen wrote:
> 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.

I'm uncertain, but perhaps pr_warn_ratelimited() would be a better
alternative to WARN_ON() here? WARN_ON_ONCE() generates warning messages
with kernel call traces in the kernel messages, which might lead users
to believe that something serious has happened in the kernel.

> 
> 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>
> ---
>   drivers/iommu/iommufd/io_pagetable.h    |   8 ++
>   drivers/iommu/iommufd/iommufd_private.h |   6 ++
>   drivers/iommu/iommufd/device.c          | 117 ++----------------------
>   drivers/iommu/iommufd/io_pagetable.c    |  95 +++++++++++++++++++
>   4 files changed, 117 insertions(+), 109 deletions(-)

Thanks,
baolu