[PATCH] swiotlb: use the adjusted address for the highmem page lookup

[Donggeun Yoo <donggeunyoo.kernel@gmail.com>]

swiotlb_bounce() reads the page frame number from the slot's recorded
orig_addr, then advances orig_addr by tlb_offset to reach the address
the caller asked about. The highmem branch mixes the two: the offset
within the page comes from the adjusted address, the page from the value
before it.

Once the adjustment crosses a page boundary the pair no longer describes
one location, and the whole copy lands one page below the intended one
for a positive tlb_offset, one above for a negative one. DMA_FROM_DEVICE
writes the device data over the wrong page and leaves the intended one
stale, DMA_TO_DEVICE feeds the device from a page the mapping may not
cover. Partial syncs through dma_sync_single_range_for_*() are what make
tlb_offset non-zero.

The branch test is picked the same way, so a slot recorded in lowmem can
be adjusted into highmem and the lowmem path then hands a highmem
address to phys_to_virt().

Take both from orig_addr once it is final and keep pfn in the branch
that uses it. PhysHighMem() asks the question straight from the address,
as dma-debug already does.

Fixes: 5f89468e2f06 ("swiotlb: manipulate orig_addr when tlb_addr has offset")
Cc: stable@vger.kernel.org
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
---
Reproduced under QEMU (qemu-system-arm -M virt, 2G) with a 32-bit ARM
kernel built from multi_v7_defconfig plus CONFIG_ARM_LPAE=y and
CONFIG_HIGHMEM=y, which brings in CONFIG_SWIOTLB, booted with
swiotlb=force. A test module maps two highmem pages at page offset 3840,
writes a pattern into the bounce buffer 500 bytes in and calls
dma_sync_single_range_for_cpu() over that range, so that 3840 + 500
crosses into the second page:

  before: swbug: pages pfn=700d4 highmem=1
          swbug: orig phys=700d4f00 (page off 3840)
          swbug: RESULT page0_off=244 page1_off=-1
  after:  swbug: RESULT page0_off=-1 page1_off=244

The pattern lands one page below its intended location without the
change and in the right place with it.

 kernel/dma/swiotlb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index ded7016a46a7..aa2f1c4588b9 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1019,7 +1019,6 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 	int index = (tlb_addr - mem->start) >> IO_TLB_SHIFT;
 	phys_addr_t orig_addr = mem->slots[index].orig_addr;
 	size_t alloc_size = mem->slots[index].alloc_size;
-	unsigned long pfn = PFN_DOWN(orig_addr);
 	unsigned char *vaddr = mem->vaddr + tlb_addr - mem->start;
 	int tlb_offset;
 
@@ -1052,7 +1051,8 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 		size = alloc_size;
 	}
 
-	if (PageHighMem(pfn_to_page(pfn))) {
+	if (PhysHighMem(orig_addr)) {
+		unsigned long pfn = PFN_DOWN(orig_addr);
 		unsigned int offset = orig_addr & ~PAGE_MASK;
 		struct page *page;
 		unsigned int sz = 0;
-- 
2.53.0