[PATCH] iommu/arm-smmu-v3: Fix big-endian CMD_SYNC writes

[PATCH] iommu/arm-smmu-v3: Fix big-endian CMD_SYNC writes

[Robin Murphy]

When we insert the sync sequence number into the CMD_SYNC.MSIData field,
we do so in CPU-native byte order, before writing out the whole command
as explicitly little-endian dwords. Thus on big-endian systems, the SMMU
will receive and write back a byteswapped version of sync_nr, which would
be perfect if it were targeting a similarly-little-endian ITS, but since
it's actually writing back to memory being polled by the CPUs, they're
going to end up seeing the wrong thing.

Since the SMMU doesn't care what the MSIData actually contains, the
minimal-overhead solution is to simply add an extra byteswap initially,
such that it then writes back the big-endian format directly.

Fixes: 37de98f8f1cf ("iommu/arm-smmu-v3: Use CMD_SYNC completion MSI")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/arm-smmu-v3.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index db402e8b068b..867ba548c2cc 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -952,7 +952,7 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu)
 	struct arm_smmu_cmdq_ent ent = {
 		.opcode = CMDQ_OP_CMD_SYNC,
 		.sync	= {
-			.msiaddr = virt_to_phys(&smmu->sync_count),
+			.msiaddr = cpu_to_le32(virt_to_phys(&smmu->sync_count)),
 		},
 	};
 
-- 
2.19.1.dirty

[PATCH] iommu/arm-smmu-v3: Fix big-endian CMD_SYNC writes

[Will Deacon]

On Tue, Oct 16, 2018 at 12:31:07PM +0100, Robin Murphy wrote:
> When we insert the sync sequence number into the CMD_SYNC.MSIData field,
> we do so in CPU-native byte order, before writing out the whole command
> as explicitly little-endian dwords. Thus on big-endian systems, the SMMU
> will receive and write back a byteswapped version of sync_nr, which would
> be perfect if it were targeting a similarly-little-endian ITS, but since
> it's actually writing back to memory being polled by the CPUs, they're
> going to end up seeing the wrong thing.
> 
> Since the SMMU doesn't care what the MSIData actually contains, the
> minimal-overhead solution is to simply add an extra byteswap initially,
> such that it then writes back the big-endian format directly.
> 
> Fixes: 37de98f8f1cf ("iommu/arm-smmu-v3: Use CMD_SYNC completion MSI")
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/arm-smmu-v3.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index db402e8b068b..867ba548c2cc 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -952,7 +952,7 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu)
>  	struct arm_smmu_cmdq_ent ent = {
>  		.opcode = CMDQ_OP_CMD_SYNC,
>  		.sync	= {
> -			.msiaddr = virt_to_phys(&smmu->sync_count),
> +			.msiaddr = cpu_to_le32(virt_to_phys(&smmu->sync_count)),

Hmm, aren't you swabbing the address here? Don't we want to swab the data?
We also need a comment to explain this!

Will

[PATCH] iommu/arm-smmu-v3: Fix big-endian CMD_SYNC writes

[Robin Murphy]

On 17/10/18 18:07, Will Deacon wrote:
> On Tue, Oct 16, 2018 at 12:31:07PM +0100, Robin Murphy wrote:
>> When we insert the sync sequence number into the CMD_SYNC.MSIData field,
>> we do so in CPU-native byte order, before writing out the whole command
>> as explicitly little-endian dwords. Thus on big-endian systems, the SMMU
>> will receive and write back a byteswapped version of sync_nr, which would
>> be perfect if it were targeting a similarly-little-endian ITS, but since
>> it's actually writing back to memory being polled by the CPUs, they're
>> going to end up seeing the wrong thing.
>>
>> Since the SMMU doesn't care what the MSIData actually contains, the
>> minimal-overhead solution is to simply add an extra byteswap initially,
>> such that it then writes back the big-endian format directly.
>>
>> Fixes: 37de98f8f1cf ("iommu/arm-smmu-v3: Use CMD_SYNC completion MSI")
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>   drivers/iommu/arm-smmu-v3.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index db402e8b068b..867ba548c2cc 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -952,7 +952,7 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu)
>>   	struct arm_smmu_cmdq_ent ent = {
>>   		.opcode = CMDQ_OP_CMD_SYNC,
>>   		.sync	= {
>> -			.msiaddr = virt_to_phys(&smmu->sync_count),
>> +			.msiaddr = cpu_to_le32(virt_to_phys(&smmu->sync_count)),
> 
> Hmm, aren't you swabbing the address here? Don't we want to swab the data?
> We also need a comment to explain this!

It's entirely possible that I'm a spectacular idiot. <sigh>

Let me try again...

Robin.