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Subject[PATCH v5] dma-debug: fix incorrect pfn calculation
Date
From: Miles Chen <miles.chen@mediatek.com>

dma-debug reports the following warning:

[name:panic&]WARNING: CPU: 3 PID: 298 at kernel-4.4/lib/dma-debug.c:604
debug _dma_assert_idle+0x1a8/0x230()
DMA-API: cpu touching an active dma mapped cacheline [cln=0x00000882300]
CPU: 3 PID: 298 Comm: vold Tainted: G W O 4.4.22+ #1
Hardware name: MT6739 (DT)
Call trace:
[<ffffff800808acd0>] dump_backtrace+0x0/0x1d4
[<ffffff800808affc>] show_stack+0x14/0x1c
[<ffffff800838019c>] dump_stack+0xa8/0xe0
[<ffffff80080a0594>] warn_slowpath_common+0xf4/0x11c
[<ffffff80080a061c>] warn_slowpath_fmt+0x60/0x80
[<ffffff80083afe24>] debug_dma_assert_idle+0x1a8/0x230
[<ffffff80081dca9c>] wp_page_copy.isra.96+0x118/0x520
[<ffffff80081de114>] do_wp_page+0x4fc/0x534
[<ffffff80081e0a14>] handle_mm_fault+0xd4c/0x1310
[<ffffff8008098798>] do_page_fault+0x1c8/0x394
[<ffffff800808231c>] do_mem_abort+0x50/0xec

I found that debug_dma_alloc_coherent() and debug_dma_free_coherent()
assume that dma_alloc_coherent() always returns a linear address. However
it's possible that dma_alloc_coherent() returns a non-linear address. In
this case, page_to_pfn(virt_to_page(virt)) will return an incorrect pfn.
If the pfn is valid and mapped as a COW page, we will hit the warning when
doing wp_page_copy().

Fix this by calculating pfn for linear and non-linear addresses.

Some changes are added to this patch according to Christoph's comment
in patch v3 and a bugfix in patch v4:
a. use normal if/else statement for better readability
b. exclude non-linear and non-vmalloc addresses
c. use virt_addr_valid() to check linear addresses

Signed-off-by: Miles Chen <miles.chen@mediatek.com>
---
lib/dma-debug.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index ea4cc3d..4c08eb6 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -1495,14 +1495,22 @@ void debug_dma_alloc_coherent(struct device *dev, size_t size,
if (!entry)
return;

+ /* handle vmalloc and linear addresses */
+ if (!is_vmalloc_addr(virt) && !virt_addr_valid(virt))
+ return;
+
entry->type = dma_debug_coherent;
entry->dev = dev;
- entry->pfn = page_to_pfn(virt_to_page(virt));
entry->offset = offset_in_page(virt);
entry->size = size;
entry->dev_addr = dma_addr;
entry->direction = DMA_BIDIRECTIONAL;

+ if (is_vmalloc_addr(virt))
+ entry->pfn = vmalloc_to_pfn(virt);
+ else
+ entry->pfn = page_to_pfn(virt_to_page(virt));
+
add_dma_entry(entry);
}
EXPORT_SYMBOL(debug_dma_alloc_coherent);
@@ -1513,13 +1521,21 @@ void debug_dma_free_coherent(struct device *dev, size_t size,
struct dma_debug_entry ref = {
.type = dma_debug_coherent,
.dev = dev,
- .pfn = page_to_pfn(virt_to_page(virt)),
.offset = offset_in_page(virt),
.dev_addr = addr,
.size = size,
.direction = DMA_BIDIRECTIONAL,
};

+ /* handle vmalloc and linear addresses */
+ if (!is_vmalloc_addr(virt) && !virt_addr_valid(virt))
+ return;
+
+ if (is_vmalloc_addr(virt))
+ ref.pfn = vmalloc_to_pfn(virt);
+ else
+ ref.pfn = page_to_pfn(virt_to_page(virt));
+
if (unlikely(dma_debug_disabled()))
return;

--
1.9.1
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