[PATCH 5.15.y v3 0/1] Manual Backport of 099606a7b2d5 to 5.15

[PATCH 5.15.y v3 0/1] Manual Backport of 099606a7b2d5 to 5.15

[Harshvardhan Jha]

The patch 099606a7b2d5 didn't cleanly apply to 5.15 due to the
significant difference in codebases.

I've tried to manually bring it back to 5.15 via some minor conflict
resolution but also invoking the newly introduced API using inverted
logic as the conditional statements present in 5.15 are the opposite of
those in 6.1 xen/swiotlib.

v2 of this patch was added and dropped due to some issues in testing.
However, after further verification this version seems to be right as
is.

I kindly request Juergen's ack specifically before this is added to
stable queue as this patch differs quite significantly compared to the
original.

Changes in v2:
Include correct upstream SHA in the commit message

Changes in v3:
Patch remains the same, however further verification and testing was
done.

Harshvardhan Jha (1):
  xen/swiotlb: relax alignment requirements

 drivers/xen/swiotlb-xen.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

-- 
2.47.1

[PATCH 5.15.y v3 1/1] xen/swiotlb: relax alignment requirements

[Harshvardhan Jha]

[ 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")

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Harshvardhan Jha <harshvardhan.j.jha@oracle.com>
---
 drivers/xen/swiotlb-xen.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 0392841a822fa..65da97be06285 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -75,19 +75,21 @@ 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;
@@ -306,7 +308,8 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 	phys = dma_to_phys(hwdev, *dma_handle);
 	dev_addr = xen_phys_to_dma(hwdev, phys);
 	if (((dev_addr + size - 1 <= dma_mask)) &&
-	    !range_straddles_page_boundary(phys, size))
+	    !range_straddles_page_boundary(phys, size) &&
+	    !range_requires_alignment(phys, size))
 		*dma_handle = dev_addr;
 	else {
 		if (xen_create_contiguous_region(phys, order,
@@ -347,6 +350,7 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 
 	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
 		     range_straddles_page_boundary(phys, size)) &&
+	    !range_requires_alignment(phys, size) &&
 	    TestClearPageXenRemapped(page))
 		xen_destroy_contiguous_region(phys, order);
 
-- 
2.47.1

Re: [PATCH 5.15.y v3 1/1] xen/swiotlb: relax alignment requirements

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 85fcb57c983f423180ba6ec5d0034242da05cc54

WARNING: Author mismatch between patch and upstream commit:
Backport author: Harshvardhan Jha<harshvardhan.j.jha@oracle.com>
Commit author: Juergen Gross<jgross@suse.com>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.12.y | Present (different SHA1: 5a10af375347)
6.6.y | Present (different SHA1: 461d9e8acaa4)
6.1.y | Present (different SHA1: 099606a7b2d5)

Note: The patch differs from the upstream commit:
---
1:  85fcb57c983f4 ! 1:  d8109ab010afb xen/swiotlb: relax alignment requirements
    @@
      ## Metadata ##
    -Author: Juergen Gross <jgross@suse.com>
    +Author: Harshvardhan Jha <harshvardhan.j.jha@oracle.com>
     
      ## Commit message ##
         xen/swiotlb: relax alignment requirements
     
    +    [ 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
    @@ Commit message
         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: Harshvardhan Jha <harshvardhan.j.jha@oracle.com>
     
      ## drivers/xen/swiotlb-xen.c ##
     @@ drivers/xen/swiotlb-xen.c: static inline phys_addr_t xen_dma_to_phys(struct device *dev,
    @@ drivers/xen/swiotlb-xen.c: static inline phys_addr_t xen_dma_to_phys(struct devi
      	for (i = 1; i < nr_pages; i++)
      		if (pfn_to_bfn(++xen_pfn) != ++next_bfn)
      			return 1;
    -@@ drivers/xen/swiotlb-xen.c: 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;
    -@@ drivers/xen/swiotlb-xen.c: xen_swiotlb_free_coherent(struct device *dev, size_t size, void *vaddr,
    - 	size = ALIGN(size, XEN_PAGE_SIZE);
    +@@ drivers/xen/swiotlb-xen.c: xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
    + 	phys = dma_to_phys(hwdev, *dma_handle);
    + 	dev_addr = xen_phys_to_dma(hwdev, phys);
    + 	if (((dev_addr + size - 1 <= dma_mask)) &&
    +-	    !range_straddles_page_boundary(phys, size))
    ++	    !range_straddles_page_boundary(phys, size) &&
    ++	    !range_requires_alignment(phys, size))
    + 		*dma_handle = dev_addr;
    + 	else {
    + 		if (xen_create_contiguous_region(phys, order,
    +@@ drivers/xen/swiotlb-xen.c: xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
      
    - 	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 (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
    + 		     range_straddles_page_boundary(phys, size)) &&
    ++	    !range_requires_alignment(phys, size) &&
    + 	    TestClearPageXenRemapped(page))
    + 		xen_destroy_contiguous_region(phys, order);
      
    - 	if (TestClearPageXenRemapped(virt_to_page(vaddr)))
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.15.y       |  Success    |  Success   |