Re: [PATCH v2 1/2] xen/swiotlb: add alignment check for dma buffers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.09.2024 08:47, Juergen Gross wrote:
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -78,9 +78,15 @@ static inline int 
> range_straddles_page_boundary(phys_addr_t p, size_t size)
>  {
>       unsigned long next_bfn, xen_pfn = XEN_PFN_DOWN(p);
>       unsigned int i, nr_pages = XEN_PFN_UP(xen_offset_in_page(p) + size);
> +     phys_addr_t algn = 1ULL << (get_order(size) + PAGE_SHIFT);
>  
>       next_bfn = pfn_to_bfn(xen_pfn);
>  
> +     /* If buffer is physically aligned, ensure DMA alignment. */
> +     if (IS_ALIGNED(p, algn) &&
> +         !IS_ALIGNED(next_bfn << XEN_PAGE_SHIFT, algn))

And this shift is not at risk of losing bits on Arm LPAE?

Jan