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Re: [PATCH v2 1/2] xen/swiotlb: add alignment check for dma buffers
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Jürgen Groß <jgross@xxxxxxxx>
- Date: Mon, 16 Sep 2024 09:02:56 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, iommu@xxxxxxxxxxxxxxx
- Delivery-date: Mon, 16 Sep 2024 07:03:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.09.24 08:59, Jan Beulich wrote:
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"?
No, this wouldn't work in case algn < XEN_PAGE_SIZE.
Juergen
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