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

[Dominique MARTINET]

Jianxiong Gao wrote on Fri, Jun 18, 2021 at 11:01:59AM -0700:
> > Jianxiong Gao, before spending more time on this, could you also try
> > Chanho Park's patch?
> > https://lore.kernel.org/linux-iommu/20210510091816.GA2084@xxxxxx/T/#m0d0df6490350a08dcc24c9086c8edc165b402d6f
> >
> I have tested Chanho Parks's patch and it works for us.
> The NVMe driver performs correctly with the patch.
> 
> I have teste the patch on 06af8679449d

Thanks!
(a bit late, but added Chanho Park in Cc...)

I can confirm it also works for our caam problem, as Horia said.

I've also come to term with the use of swiotlb_align_offset() through
testing, or rather many devices seem to have a 0 mask so it will almost
always be cancelled out, so if it works for Jianxiong then it's probably
good enough and I'll just assume that's how the orig_addr has been
designed...

I think it's missing a couple of checks like the one Linus had in his
patch, and would be comfortable with something like the attached patch
(in practice for me exactly the same as the original patch, except I've
added two checks: offsets smaller than orig addr offset are refused as
well as offsets bigger than the mapping size)

I'm sorry Jianxiong but would you be willing to take the time to test
again just to make sure there were no such offsets in your case?


If we're good with that I'll send it as an official v2 keeping Chanho's
from, unless he wants to.


Thanks everyone,
-- 
Dominique


diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 8ca7d505d61c..23f8d0b168c5 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -334,6 +334,14 @@ void __init swiotlb_exit(void)
 	io_tlb_default_mem = NULL;
 }
 
+/*
+ * Return the offset into a iotlb slot required to keep the device happy.
+ */
+static unsigned int swiotlb_align_offset(struct device *dev, u64 addr)
+{
+	return addr & dma_get_min_align_mask(dev) & (IO_TLB_SIZE - 1);
+}
+
 /*
  * Bounce: copy the swiotlb buffer from or back to the original dma location
  */
@@ -346,10 +354,31 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 	size_t alloc_size = mem->slots[index].alloc_size;
 	unsigned long pfn = PFN_DOWN(orig_addr);
 	unsigned char *vaddr = phys_to_virt(tlb_addr);
+	unsigned int tlb_offset, orig_addr_offset;
 
 	if (orig_addr == INVALID_PHYS_ADDR)
 		return;
 
+	tlb_offset = tlb_addr & (IO_TLB_SIZE - 1);
+	orig_addr_offset = swiotlb_align_offset(dev, orig_addr);
+	if (tlb_offset < orig_addr_offset) {
+		dev_WARN_ONCE(dev, 1,
+			"Access before mapping start detected. orig offset %u, requested offset %u.\n",
+			orig_addr_offset, tlb_offset);
+		return;
+	}
+
+	tlb_offset -= orig_addr_offset;
+	if (tlb_offset > alloc_size) {
+		dev_WARN_ONCE(dev, 1,
+			"Buffer overflow detected. Allocation size: %zu. Mapping size: %zu+%u.\n",
+			alloc_size, size, tlb_offset);
+		return;
+	}
+
+	orig_addr += tlb_offset;
+	alloc_size -= tlb_offset;
+
 	if (size > alloc_size) {
 		dev_WARN_ONCE(dev, 1,
 			"Buffer overflow detected. Allocation size: %zu. Mapping size: %zu.\n",
@@ -390,14 +419,6 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 
 #define slot_addr(start, idx)	((start) + ((idx) << IO_TLB_SHIFT))
 
-/*
- * Return the offset into a iotlb slot required to keep the device happy.
- */
-static unsigned int swiotlb_align_offset(struct device *dev, u64 addr)
-{
-	return addr & dma_get_min_align_mask(dev) & (IO_TLB_SIZE - 1);
-}
-
 /*
  * Carefully handle integer overflow which can occur when boundary_mask == ~0UL.
  */