On 16.09.2024 08:56, Juergen Gross wrote:
> On 16.09.24 08:50, Jan Beulich wrote:
>> 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?
>
> For alignment check this just doesn't matter (assuming XEN_PAGE_SIZE is
> smaller than 4G).
Oh, yes - of course. A (hypothetical?) strict no-overflow checking
mode of the kernel may take issue though, so maybe better to right-
shift "algn"?
Jan
