From: Jason Gunthorpe <jgg@ziepe.ca>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "zhangzekun (A)" <zhangzekun11@huawei.com>,
will@kernel.org, joro@8bytes.org, nicolinc@nvidia.com,
mshavit@google.com, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu-v3: Add a threshold to avoid potential soft lockup
Date: Wed, 24 Jan 2024 12:28:08 -0400 [thread overview]
Message-ID: <20240124162808.GT50608@ziepe.ca> (raw)
In-Reply-To: <10c1980a-df07-4f69-93e5-c1c50b106a13@arm.com>
On Wed, Jan 24, 2024 at 12:17:43PM +0000, Robin Murphy wrote:
> I don't think the story here has changed from when I first remember this
> being discussed probably 7 or 8 years ago - what VFIO has always really
> wanted for this situation is to know when it's doing a complete teardown and
> just detach and free the domain, then unpin the pages afterwards, without
> wasting any time at all on frivolous unmapping.
What VFIO/iommufd really wants is a fast way to to read back and unmap
the PFNs from the domain. Today it has to call iommu_iova_to_phys()
and then unmap which ends up walking the radix many times.
Ideally we'd batch read and unmap in a single call with a single radix
walk.
This is because the domain is used to store the 'struct page *' which
is needed to unpin the memory.
Combined with the no-attachments optimization I described it could be
pretty close to optimal.
Jason
prev parent reply other threads:[~2024-01-24 16:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-15 11:40 [PATCH] iommu/arm-smmu-v3: Add a threshold to avoid potential soft lockup Zhang Zekun
2024-01-15 15:31 ` Jason Gunthorpe
2024-01-18 11:21 ` zhangzekun (A)
2024-01-18 14:22 ` Jason Gunthorpe
2024-01-24 12:17 ` Robin Murphy
2024-01-24 16:28 ` Jason Gunthorpe [this message]
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