Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing

[Will Deacon]

On Wed, Jun 23, 2021 at 12:39:29PM -0400, Qian Cai wrote:
> 
> 
> On 6/18/2021 11:40 PM, Claire Chang wrote:
> > Propagate the swiotlb_force into io_tlb_default_mem->force_bounce and
> > use it to determine whether to bounce the data or not. This will be
> > useful later to allow for different pools.
> > 
> > Signed-off-by: Claire Chang <tientzu@xxxxxxxxxxxx>
> > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Tested-by: Will Deacon <will@xxxxxxxxxx>
> > Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> 
> Reverting the rest of the series up to this patch fixed a boot crash with NVMe on today's linux-next.

Hmm, so that makes patch 7 the suspicious one, right?

Looking at that one more closely, it looks like swiotlb_find_slots() takes
'alloc_size + offset' as its 'alloc_size' parameter from
swiotlb_tbl_map_single() and initialises 'mem->slots[i].alloc_size' based
on 'alloc_size + offset', which looks like a change in behaviour from the
old code, which didn't include the offset there.

swiotlb_release_slots() then adds the offset back on afaict, so we end up
accounting for it twice and possibly unmap more than we're supposed to?

Will