[PATCH] iommu/arm-smmu: Allow size of stage 1 output to max possible value for sateg 2 bypass

[tirumalesh chalamarla]

Hi Will,


On Mon, Sep 1, 2014 at 4:42 AM, Will Deacon <will.deacon at arm.com> wrote:
> Hi Tirumalesh,
>
> On Wed, Aug 27, 2014 at 07:02:21PM +0100, c.tirumalesh at gmail.com wrote:
>> From: Tirumalesh Chalamarla <tchalamarla at cavium.com>
>>
>> This patch modifes output_mask calculation logic for stage 1 and allow
>> max possible value supported by SMMU implementaions for translations,
>> where stage 2 is bypassed.
>>
>> Erlier it is not possible to access full supported PA address with stage 1,
>> even if it is supported by SMMU and stage 2 is bypass.
>
> I'm trying to understand what you're getting at here. Essentially, you want
> to use the full stage-1 output range for a stage-1 only MMU, right?
>

YES,  restrict stage 1 out put to VA_BITS only if stage 2 is needed
(i.e for NESTED_TRANSLATIONS).

> The code is currently structured to truncate that to the stage-2 input size
> for nested translation. However, I think that's better solved by faking the
> ID registers in the virtual SMMU instead of posing these restrictions on the
> host as well.
>

This sounds good, the only problem is, it is too much bound to virtual
SMMU. There is no harm in changing/checking the
stage 1 output mask, if stage 2 present, in host also.


> Assuming I understand the problem correctly, why not simply remove the
> truncation from the existing code (untested patch below)? Does that not
> work for you?
>

This will not restrict stage 1 out put to VA_BITS, even for two level
translations. this results in non debuggable problems
if we configure incorrectly.  there is no harm in checking the
condition for nested translations, as i did in my patch.


Regards,
Tirumalesh.

> Will
>
> --->8
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 2b1271658bfa..a02d05793a73 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1917,21 +1917,7 @@ static int arm_smmu_device_cfg_probe(struct arm_smmu_device *smmu)
>         /* ID2 */
>         id = readl_relaxed(gr0_base + ARM_SMMU_GR0_ID2);
>         size = arm_smmu_id_size_to_bits((id >> ID2_IAS_SHIFT) & ID2_IAS_MASK);
> -
> -       /*
> -        * Stage-1 output limited by stage-2 input size due to pgd
> -        * allocation (PTRS_PER_PGD).
> -        */
> -       if (smmu->features & ARM_SMMU_FEAT_TRANS_NESTED) {
> -#ifdef CONFIG_64BIT
> -               smmu->s1_output_size = min_t(unsigned long, VA_BITS, size);
> -#else
> -               smmu->s1_output_size = min(32UL, size);
> -#endif
> -       } else {
> -               smmu->s1_output_size = min_t(unsigned long, PHYS_MASK_SHIFT,
> -                                            size);
> -       }
> +       smmu->s1_output_size = min_t(unsigned long, PHYS_MASK_SHIFT, size);
>
>         /* The stage-2 output mask is also applied for bypass */
>         size = arm_smmu_id_size_to_bits((id >> ID2_OAS_SHIFT) & ID2_OAS_MASK);