swiotlb: reduce the swiotlb buffer size on allocation failure

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At the moment the AMD encrypted platform reserves 6% of RAM for SWIOTLB
or 1GB, whichever is less. However it is possible that there is no block
big enough in the low memory which make SWIOTLB allocation fail and
the kernel continues without DMA. In such case a VM hangs on DMA.

This moves alloc+remap to a helper and calls it from a loop where
the size is halved on each iteration.

This updates default_nslabs on successful allocation which looks like
an oversight as not doing so should have broken callers of
swiotlb_size_or_default().

Signed-off-by: Alexey Kardashevskiy <aik@amd.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

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This commit is contained in:

Alexey Kardashevskiy 2022-10-31 19:13:27 +11:00 • committed by Christoph Hellwig

parent 30a0b95b13

commit 8d58aa4849

1 changed files with 39 additions and 24 deletions

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kernel/dma/swiotlb.c

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