Re: [PATCH v2 2/2] iommu/arm-smmu-v3: Add HAFT support for SVA

[Robin Murphy <robin.murphy@arm.com>]

On 27/07/2026 9:12 am, Will Deacon wrote:
> On Sun, Jul 26, 2026 at 01:10:19PM -0300, Jason Gunthorpe wrote:
>> On Sun, Jul 26, 2026 at 01:00:38PM +0100, Will Deacon wrote:
>>> On Sat, Jul 25, 2026 at 11:27:59AM -0300, Jason Gunthorpe wrote:
>>>> On Thu, Jul 23, 2026 at 03:19:44PM +0100, Robin Murphy wrote:
>>>>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
>>>>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
>>>>> @@ -102,6 +102,8 @@ void arm_smmu_make_sva_cd(struct arm_smmu_cd *target,
>>>>>   			target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HA);
>>>>>   		if (master->smmu->features & ARM_SMMU_FEAT_HD)
>>>>>   			target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HD);
>>>>> +		if (master->smmu->features & ARM_SMMU_FEAT_HAFT && system_supports_haft())
>>>>> +			target->data[1] |= cpu_to_le64(CTXDESC_CD_1_HAFT);
>>>>>   	} else {
>>>>>   		target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_EPD0);
>>>>
>>>> Based on the Sashiko remark and your note you should lift all the
>>>> HA/HD/HAFT bits outside this if (mm) block.
>>>>
>>>> AFAICT it is fine for HA/HD/HAFT to be set with EPD0, the HW won't
>>>> process any PTEs so they won't have any effect.
>>>
>>> I'm not sure about that. The spec says this about CD.HAFT:
>>
>> Sorry I see this was unclear
>>
>> I ment to move all *three* bits outside the if.
>>
>> There is no reason for EPD0 to also require setting any of those three
>> bits to zero, AFAICT.
> 
> Ah, gotcha! And even if we did want to get to that configuration, I
> guess you could set EPD0, then clear HAFT, then clear HA+HD?

Indeed, it also occurred to me on the way home on Friday that in this 
case we probably could get away with just setting HA/HD/HAFT 
consistently in all SVA CDs irrespective of the mm. Strictly, EPD0 only 
forbids *new* walks from using TTB0, so there might potentially be some 
outstanding PTE updates still made in the window between the config 
update and the TLBI at the end of arm_smmu_mm_release(), but that 
shouldn't be harmful.

Lemme spin a v3...

Cheers,
Robin.