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

On 2021-06-24 12:18, Will Deacon wrote:
On Thu, Jun 24, 2021 at 12:14:39PM +0100, Robin Murphy wrote:
On 2021-06-24 07:05, Claire Chang wrote:
On Thu, Jun 24, 2021 at 1:43 PM Christoph Hellwig <hch@xxxxxx> wrote:

On Wed, Jun 23, 2021 at 02:44:34PM -0400, Qian Cai wrote:
is_swiotlb_force_bounce at /usr/src/linux-next/./include/linux/swiotlb.h:119

is_swiotlb_force_bounce() was the new function introduced in this patch here.

+static inline bool is_swiotlb_force_bounce(struct device *dev)
+     return dev->dma_io_tlb_mem->force_bounce;

To me the crash looks like dev->dma_io_tlb_mem is NULL.  Can you
turn this into :

          return dev->dma_io_tlb_mem && dev->dma_io_tlb_mem->force_bounce;

for a quick debug check?

I just realized that dma_io_tlb_mem might be NULL like Christoph
pointed out since swiotlb might not get initialized.
However,  `Unable to handle kernel paging request at virtual address
dfff80000000000e` looks more like the address is garbage rather than
I wonder if that's because dev->dma_io_tlb_mem is not assigned
properly (which means device_initialize is not called?).

What also looks odd is that the base "address" 0xdfff800000000000 is held in
a couple of registers, but the offset 0xe looks too small to match up to any
relevant structure member in that dereference chain :/

FWIW, I've managed to trigger a NULL dereference locally when swiotlb hasn't
been initialised but we dereference 'dev->dma_io_tlb_mem', so I think
Christoph's suggestion is needed regardless.

Ack to that - for SWIOTLB_NO_FORCE, io_tlb_default_mem will remain NULL. The massive jump in KernelCI baseline failures as of yesterday looks like every arm64 machine with less than 4GB of RAM blowing up...


But I agree that it won't help
with the issue reported by Qian Cai.

Qian Cai: please can you share your .config and your command line?





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