On 30/10/2018 01:52, Leizhen (ThunderTown) wrote:
On 2018/10/30 1:59, Will Deacon wrote:
On Sat, Oct 20, 2018 at 03:36:54PM +0800, Zhen Lei wrote:
The standard GITS_TRANSLATER register in ITS is only 4 bytes, but
Hisilicon expands the next 4 bytes to carry some IMPDEF information. That
means, total 8 bytes data will be written to MSIAddress each time.
MSIAddr: |----4bytes----|----4bytes----|
| MSIData | IMPDEF |
There is no problem for ITS, because the next 4 bytes space is reserved
in ITS. But it will overwrite the 4 bytes memory following "sync_count".
It's very fortunately that the previous and the next neighbour of the
"sync_count" are both aligned by 8 bytes, so no problem is met now.
It's good to explicitly add a workaround:
1. Add gcc __attribute__((aligned(8))) to make sure that "sync_count" is
always aligned by 8 bytes.
2. Add a "int" struct member to make sure the 4 bytes padding is always
exist.
There is no functional change.
Signed-off-by: Zhen Lei <[email protected]>
---
drivers/iommu/arm-smmu-v3.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 5059d09..624fdd0 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -586,7 +586,20 @@ struct arm_smmu_device {
struct arm_smmu_strtab_cfg strtab_cfg;
- u32 sync_count;
+ /*
+ * The alignment and padding is required by Hi16xx of Hisilicon.
Nit: I know that there is no functional change related to this bug which
depends on the chip version, but how about "hi1620 and earlier"? hi16xx
is very broad.
Thanks
+ * Because the ITS hardware on Hi16xx will truncate the MSIAddress(Here
+ * it's the address of "sync_count") to 8 bytes boundary first, then
+ * write 32 bits MSIdata at offset 0, and 32 bits IMPDEF data at offset
+ * 4. Without this workaround, the adjacent member maybe overwritten.
+ *
+ * |---4bytes---|---4bytes---|
+ * MSIAddress & (~0x7): MSIdata | IMPDEF data|
+ */
+ struct {
+ u32 sync_count;
+ int padding;
+ } __attribute__((aligned(8)));
I thought the conclusion after reviewing your original patch was to maintain
the union and drop the alignment directive? e.g.
union {
u32 sync_count;
u64 padding; /* Hi16xx writes an extra 32 bits of goodness
*/
};
OK, I will sent v3.
Will
.
_______________________________________________
iommu mailing list
[email protected]
https://lists.linuxfoundation.org/mailman/listinfo/iommu
