Re: swiotlb/caamjr regression (Was: [GIT PULL] (swiotlb) stable/for-linus-5.12)

[Linus Torvalds <torvalds@linux-foundation.org>]

[-- Attachment #1: Type: text/plain, Size: 1249 bytes --]

On Thu, Jun 10, 2021 at 7:52 AM Horia Geantă <horia.geanta@nxp.com> wrote:
>
> Documentation/core-api/dma-api.rst explicitly allows for partial syncs:
> Synchronise a single contiguous or scatter/gather mapping for the CPU
> and device. With the sync_sg API, all the parameters must be the same
> as those passed into the single mapping API. With the sync_single API,
> you can use dma_handle and size parameters that aren't identical to
> those passed into the single mapping API to do a partial sync.
>
> AFAICS commit 16fc3cef33a0 ("swiotlb: don't modify orig_addr in swiotlb_tbl_sync_single")
> is breaking this functionality.

How about a patch like the attached? Does that fix things for you.

Christoph? Comments - that commit removed the offset calculation
entirely, because the old

        (unsigned long)tlb_addr & (IO_TLB_SIZE - 1)

was wrong, but instead of removing it, I think it should have just
fixed it to be

        (tlb_addr - mem->start) & (IO_TLB_SIZE - 1);

instead. That way the slot offset always matches the slot index calculation.

I also made it then take the offset into account for the alloc_size checks.

Does this UNTESTED patch perhaps do the right thing?

                    Linus

[-- Attachment #2: patch.diff --]
[-- Type: text/x-patch, Size: 1130 bytes --]

 kernel/dma/swiotlb.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 8ca7d505d61c..f63d15e94d35 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -342,6 +342,7 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 {
 	struct io_tlb_mem *mem = io_tlb_default_mem;
 	int index = (tlb_addr - mem->start) >> IO_TLB_SHIFT;
+	unsigned long offset = (tlb_addr - mem->start) & (IO_TLB_SIZE - 1);
 	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);
@@ -350,6 +351,14 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 	if (orig_addr == INVALID_PHYS_ADDR)
 		return;
 
+	if (offset > alloc_size) {
+		dev_WARN_ONCE(dev, 1,
+			"Buffer overflow detected. Offset: %lu. Mapping size: %zu.\n",
+			offset, size);
+		return;
+	}
+	alloc_size -= offset;
+	orig_addr += offset;
 	if (size > alloc_size) {
 		dev_WARN_ONCE(dev, 1,
 			"Buffer overflow detected. Allocation size: %zu. Mapping size: %zu.\n",