[v2,4/4] drivers: dma-coherent: use memset_io for DMA_MEMORY_IO mappings

Commit Message

Brian Starkey Feb. 29, 2016, 4:09 p.m. UTC

Use memset_io() for DMA_MEMORY_IO mappings which are mapped as I/O
memory, and regular memset() for DMA_MEMORY_MAP mappings.

This fixes the below alignment fault on arm64 for DMA_MEMORY_IO
mappings, where memset() uses the DC ZVA instruction which is
invalid on device memory.

   Unhandled fault: alignment fault (0x96000061) at 0xffffff8000380000
   Internal error: : 96000061 [#1] PREEMPT SMP
   Modules linked in: hdlcd(+) clk_scpi
   CPU: 4 PID: 1355 Comm: systemd-udevd Not tainted 4.4.0-rc1+ #5
   Hardware name: ARM Juno development board (r0) (DT)
   task: ffffffc9763eee00 ti: ffffffc9758c4000 task.ti: ffffffc9758c4000
   PC is at __efistub_memset+0x1ac/0x200
   LR is at dma_alloc_from_coherent+0xb0/0x120
   pc : [<ffffffc00030ff2c>] lr : [<ffffffc00042a918>] pstate: 400001c5
   sp : ffffffc9758c79a0
   x29: ffffffc9758c79a0 x28: ffffffc000635cd0
   x27: 0000000000000124 x26: ffffffc000119ef4
   x25: 0000000000010000 x24: 0000000000000140
   x23: ffffffc07e9ac3a8 x22: ffffffc9758c7a58
   x21: ffffffc9758c7a68 x20: 0000000000000004
   x19: ffffffc07e9ac380 x18: 0000000000000001
   x17: 0000007fae1bbba8 x16: ffffffc0001b2d1c
   x15: ffffffffffffffff x14: 0ffffffffffffffe
   x13: 0000000000000010 x12: ffffff800837ffff
   x11: ffffff800837ffff x10: 0000000040000000
   x9 : 0000000000000000 x8 : ffffff8000380000
   x7 : 0000000000000000 x6 : 000000000000003f
   x5 : 0000000000000040 x4 : 0000000000000000
   x3 : 0000000000000004 x2 : 000000000000ffc0
   x1 : 0000000000000000 x0 : ffffff8000380000

Signed-off-by: Brian Starkey <[e-mail]>
Reviewed-by: Catalin Marinas <[e-mail]>
---
 drivers/base/dma-coherent.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Andrew Morton Feb. 29, 2016, 11:17 p.m. UTC | #1

On Mon, 29 Feb 2016 16:09:24 +0000 Brian Starkey <[e-mail]> wrote:

> Use memset_io() for DMA_MEMORY_IO mappings which are mapped as I/O
> memory, and regular memset() for DMA_MEMORY_MAP mappings.
> 
> This fixes the below alignment fault on arm64 for DMA_MEMORY_IO
> mappings, where memset() uses the DC ZVA instruction which is
> invalid on device memory.

What's the urgency of this fix?  "Hair on fire needed in stable asap"
or "Nice to have in there for 4.6" or what?

Brian Starkey March 1, 2016, 9:03 a.m. UTC | #2

Hi Andrew,

On Mon, Feb 29, 2016 at 03:17:49PM -0800, Andrew Morton wrote:
>On Mon, 29 Feb 2016 16:09:24 +0000 Brian Starkey <[e-mail]> wrote:
>
>> Use memset_io() for DMA_MEMORY_IO mappings which are mapped as I/O
>> memory, and regular memset() for DMA_MEMORY_MAP mappings.
>>
>> This fixes the below alignment fault on arm64 for DMA_MEMORY_IO
>> mappings, where memset() uses the DC ZVA instruction which is
>> invalid on device memory.
>
>What's the urgency of this fix?  "Hair on fire needed in stable asap"
>or "Nice to have in there for 4.6" or what?
>

No-one else is complaining so probably not the former. If it could
make 4.6 though that would be grand.

As for stable, anything before 3.15 doesn't hit the fault (on arm64)
because memset() is different, so probably not needed there.
For anything after that this patch in isolation isn't a full fix,
because dma_init_coherent_memory() will still use the wrong mapping
function for DMA_MEMORY_MAP. In that case, I think it needs to be the
whole series or nothing. I don't have a strong opinion either way, but
perhaps someone else does.

Thanks
Brian

Patch

diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 25bb398..bdf28f7 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -187,7 +187,10 @@  int dma_alloc_from_coherent(struct device *dev, ssize_t size,
 	 */
 	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
 	*ret = mem->virt_base + (pageno << PAGE_SHIFT);
-	memset(*ret, 0, size);
+	if (mem->flags & DMA_MEMORY_MAP)
+		memset(*ret, 0, size);
+	else
+		memset_io(*ret, 0, size);
 	spin_unlock_irqrestore(&mem->spinlock, flags);
 
 	return 1;