Re: [PATCH RFC] xen/swiotlb: avoid arch_sync_dma_* on per-device DMA memory

["Jürgen Groß" <jgross@suse.com>]

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On 15.04.26 17:08, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@nxp.com>
> 
> On ARM64, arch_sync_dma_for_{cpu,device}() assumes that the
> physical address passed in refers to normal RAM that is part of the
> kernel linear(direct) mapping, as it unconditionally derives a CPU
> virtual address via phys_to_virt().
> 
> With Xen swiotlb, devices may use per-device coherent DMA memory,
> such as reserved-memory regions described by 'shared-dma-pool',
> which are assigned to dev->dma_mem. These regions may be marked
> no-map in DT and therefore are not part of the kernel linear map.
> In such cases, pfn_valid() still returns true, but phys_to_virt()
> is not valid and cache maintenance via arch_sync_dma_* will fault.
> 
> Prevent this by excluding devices with a private DMA memory pool
> (dev->dma_mem) from the arch_sync_dma_* fast path, and always
> fall back to xen_dma_sync_* for those devices to avoid invalid
> phys_to_virt() conversions for no-map DMA memory while preserving the
> existing fast path for normal, linear-mapped RAM.
> 
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
>   drivers/xen/swiotlb-xen.c | 17 +++++++++++++----
>   1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 2cbf2b588f5b20cfbf9e83a8339dc22092c9559a..b1445df99d9a8f1d18a83b8c413bada6e5579209 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -195,6 +195,11 @@ xen_swiotlb_free_coherent(struct device *dev, size_t size, void *vaddr,
>   }
>   #endif /* CONFIG_X86 */
>   
> +static inline bool dev_has_private_dma_pool(struct device *dev)
> +{
> +	return dev && dev->dma_mem;
> +}
> +

I don't think this will compile on x86.


Juergen

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