releases/6.13.4/xen-swiotlb-relax-alignment-requirements.patch

From b186063519157faadbd94c1d27e3472109690d97 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 10 Feb 2025 08:43:39 +0100
Subject: xen/swiotlb: relax alignment requirements

From: Juergen Gross <jgross@suse.com>

[ Upstream commit 85fcb57c983f423180ba6ec5d0034242da05cc54 ]

When mapping a buffer for DMA via .map_page or .map_sg DMA operations,
there is no need to check the machine frames to be aligned according
to the mapped areas size. All what is needed in these cases is that the
buffer is contiguous at machine level.

So carve out the alignment check from range_straddles_page_boundary()
and move it to a helper called by xen_swiotlb_alloc_coherent() and
xen_swiotlb_free_coherent() directly.

Fixes: 9f40ec84a797 ("xen/swiotlb: add alignment check for dma buffers")
Reported-by: Jan Vejvalka <jan.vejvalka@lfmotol.cuni.cz>
Tested-by: Jan Vejvalka <jan.vejvalka@lfmotol.cuni.cz>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/xen/swiotlb-xen.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index a337edcf8faf7..26c62e0d34e98 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -74,19 +74,21 @@ static inline phys_addr_t xen_dma_to_phys(struct device *dev,
 	return xen_bus_to_phys(dev, dma_to_phys(dev, dma_addr));
 }
 
+static inline bool range_requires_alignment(phys_addr_t p, size_t size)
+{
+	phys_addr_t algn = 1ULL << (get_order(size) + PAGE_SHIFT);
+	phys_addr_t bus_addr = pfn_to_bfn(XEN_PFN_DOWN(p)) << XEN_PAGE_SHIFT;
+
+	return IS_ALIGNED(p, algn) && !IS_ALIGNED(bus_addr, algn);
+}
+
 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((phys_addr_t)next_bfn << XEN_PAGE_SHIFT, algn))
-		return 1;
-
 	for (i = 1; i < nr_pages; i++)
 		if (pfn_to_bfn(++xen_pfn) != ++next_bfn)
 			return 1;
@@ -156,7 +158,8 @@ xen_swiotlb_alloc_coherent(struct device *dev, size_t size,
 
 	*dma_handle = xen_phys_to_dma(dev, phys);
 	if (*dma_handle + size - 1 > dma_mask ||
-	    range_straddles_page_boundary(phys, size)) {
+	    range_straddles_page_boundary(phys, size) ||
+	    range_requires_alignment(phys, size)) {
 		if (xen_create_contiguous_region(phys, order, fls64(dma_mask),
 				dma_handle) != 0)
 			goto out_free_pages;
@@ -182,7 +185,8 @@ xen_swiotlb_free_coherent(struct device *dev, size_t size, void *vaddr,
 	size = ALIGN(size, XEN_PAGE_SIZE);
 
 	if (WARN_ON_ONCE(dma_handle + size - 1 > dev->coherent_dma_mask) ||
-	    WARN_ON_ONCE(range_straddles_page_boundary(phys, size)))
+	    WARN_ON_ONCE(range_straddles_page_boundary(phys, size) ||
+			 range_requires_alignment(phys, size)))
 	    	return;
 
 	if (TestClearPageXenRemapped(virt_to_page(vaddr)))
-- 
2.39.5