Re: [PATCH] Changing the AMD IOMMU API path to work in an atomic context which is necessary for any custom drivers using the IOMMU API while holding a spinlock.

[Joerg Roedel]

On Fri, Aug 24, 2018 at 02:28:49PM +0000, murphyt7@xxxxxx wrote:
> From: Tom Murphy <murphyt7@xxxxxx>
> 
> ---
> 
> This patch allows the IOMMU API path in the AMD driver to be called
> from an atomic context.  This is useful for anyone building a driver
> which needs to call the IOMMU API while holding a spinlock.

A bit more context would be helpful here. This is a pretty intrusive
change since we will drain the memory allocators atomic pools now while
building page-tables. This needs some more justification than just 'some
drivers might need it'.

Further, if we really address this problem it needs to happen through
the IOMMU-API, because the functions you are patching are called from
iommu_map()/iommu_unmap(), and these functions are allowed to sleep.

So the required approach here would be to introduce something like
iommu_map_atomic()/iommu_unmap_atomic() and implement call-backs for
that in more than just one driver.

Regards,

	Joerg