Re: [PATCH] iommu/iova: Improve 32-bit free space estimate

[Joerg Roedel]

On Fri, Mar 04, 2022 at 07:36:46AM +0800, Miles Chen wrote:
> Hi Robin,
> 
> > For various reasons based on the allocator behaviour and typical
> > use-cases at the time, when the max32_alloc_size optimisation was
> > introduced it seemed reasonable to couple the reset of the tracked
> > size to the update of cached32_node upon freeing a relevant IOVA.
> > However, since subsequent optimisations focused on helping genuine
> > 32-bit devices make best use of even more limited address spaces, it
> > is now a lot more likely for cached32_node to be anywhere in a "full"
> > 32-bit address space, and as such more likely for space to become
> > available from IOVAs below that node being freed.
> > 
> > At this point, the short-cut in __cached_rbnode_delete_update() really
> > doesn't hold up any more, and we need to fix the logic to reliably
> > provide the expected behaviour. We still want cached32_node to only move
> > upwards, but we should reset the allocation size if *any* 32-bit space
> > has become available.
> > 
> > Reported-by: Yunfei Wang <yf.wang@xxxxxxxxxxxx>
> > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> 
> Would you mind adding:
> 
> Cc: <stable@xxxxxxxxxxxxxxx>

Applied without stable tag for now. If needed, please consider
re-sending it for stable when this patch is merged upstream.

Regards,

	Joerg