[PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

[PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

[sunil.kovvuri]

From: Sunil Goutham <sgoutham@cavium.com>

For software initiated address translation, when domain type is
IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
i.e return the same IOVA as translated address.

This patch is an extension to Will Deacon's patchset 
"Implement SMMU passthrough using the default domain".

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
---
 drivers/iommu/arm-smmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 41afb07..2f4a130 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1405,6 +1405,9 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 	struct io_pgtable_ops *ops= smmu_domain->pgtbl_ops;
 
+	if (domain->type == IOMMU_DOMAIN_IDENTITY)
+		return iova;
+
 	if (!ops)
 		return 0;
 
-- 
2.7.4

Re: [PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

[Sunil Kovvuri]

On Mon, Apr 17, 2017 at 5:27 PM,  <sunil.kovvuri@gmail.com> wrote:
> From: Sunil Goutham <sgoutham@cavium.com>
>
> For software initiated address translation, when domain type is
> IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
> i.e return the same IOVA as translated address.
>
> This patch is an extension to Will Deacon's patchset
> "Implement SMMU passthrough using the default domain".
>
> Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
> ---
>  drivers/iommu/arm-smmu.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 41afb07..2f4a130 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1405,6 +1405,9 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
>         struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>         struct io_pgtable_ops *ops= smmu_domain->pgtbl_ops;
>
> +       if (domain->type == IOMMU_DOMAIN_IDENTITY)
> +               return iova;
> +
>         if (!ops)
>                 return 0;
>
> --
> 2.7.4
>

Any comments or is this patch accepted ?

Thanks,
Sunil.

Re: [PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

[Will Deacon]

On Mon, Apr 17, 2017 at 05:27:26PM +0530, sunil.kovvuri@gmail.com wrote:
> From: Sunil Goutham <sgoutham@cavium.com>
> 
> For software initiated address translation, when domain type is
> IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
> i.e return the same IOVA as translated address.
> 
> This patch is an extension to Will Deacon's patchset 
> "Implement SMMU passthrough using the default domain".

Are you actually seeing an issue here? If so, why isn't SMMUv3 affected too?

> Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
> ---
>  drivers/iommu/arm-smmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 41afb07..2f4a130 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1405,6 +1405,9 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
>  	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>  	struct io_pgtable_ops *ops= smmu_domain->pgtbl_ops;
>  
> +	if (domain->type == IOMMU_DOMAIN_IDENTITY)
> +		return iova;
> +
>  	if (!ops)
>  		return 0;

I'd have thought ops would be NULL, since arm_smmu_init_domain_context
doesn't allocate them for an identity domain.

I don't understand this patch. Please can you explain the problem more
clearly?

Will

Re: [PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

[Sunil Kovvuri]

On Mon, Apr 24, 2017 at 8:14 PM, Will Deacon <will.deacon@arm.com> wrote:
> On Mon, Apr 17, 2017 at 05:27:26PM +0530, sunil.kovvuri@gmail.com wrote:
>> From: Sunil Goutham <sgoutham@cavium.com>
>>
>> For software initiated address translation, when domain type is
>> IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
>> i.e return the same IOVA as translated address.
>>
>> This patch is an extension to Will Deacon's patchset
>> "Implement SMMU passthrough using the default domain".
>
> Are you actually seeing an issue here? If so, why isn't SMMUv3 affected too?
Yes and SMMUv3 should also be effected but as of now I don't see any use case.
If needed, i can re-submit the patch with changes in SMMUv3 as well.

>
>> Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
>> ---
>>  drivers/iommu/arm-smmu.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 41afb07..2f4a130 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -1405,6 +1405,9 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
>>       struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>>       struct io_pgtable_ops *ops= smmu_domain->pgtbl_ops;
>>
>> +     if (domain->type == IOMMU_DOMAIN_IDENTITY)
>> +             return iova;
>> +
>>       if (!ops)
>>               return 0;
>
> I'd have thought ops would be NULL, since arm_smmu_init_domain_context
> doesn't allocate them for an identity domain.
Yes ops is set to NULL.

>
> I don't understand this patch. Please can you explain the problem more
> clearly?
AFAIK for any driver outside IOMMU there is only one way to identify
if device is attached to
IOMMU or not and that is by checking iommu_domain. And I don't think
it would be appropriate
for the driver to check domain->type before calling 'iommu_iova_to_phys()' API.

The difference between IOMMU disabled and IOMMU being in passthrough
mode is that, in the
later case device is still attached to default domain but in former's
case it's NULL. So there is no
way to differentiate for the external driver whether IOMMU is in
passthrough mode or DMA mode.

And since ops is NULL in passthrough mode, 'iommu_iova_to_phys()' will
return zero.

Use case for your reference
https://lkml.org/lkml/2017/3/7/299
This driver is for a NIC interface on platform which supports SMMUv2.

Let me know if any more details are needed.

Thanks,
Sunil.

>
> Will

Re: [PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

[Will Deacon]

On Mon, Apr 24, 2017 at 09:23:16PM +0530, Sunil Kovvuri wrote:
> On Mon, Apr 24, 2017 at 8:14 PM, Will Deacon <will.deacon@arm.com> wrote:
> > On Mon, Apr 17, 2017 at 05:27:26PM +0530, sunil.kovvuri@gmail.com wrote:
> >> From: Sunil Goutham <sgoutham@cavium.com>
> >>
> >> For software initiated address translation, when domain type is
> >> IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
> >> i.e return the same IOVA as translated address.
> >>
> >> This patch is an extension to Will Deacon's patchset
> >> "Implement SMMU passthrough using the default domain".
> >
> > Are you actually seeing an issue here? If so, why isn't SMMUv3 affected too?
> Yes and SMMUv3 should also be effected but as of now I don't see any use case.
> If needed, i can re-submit the patch with changes in SMMUv3 as well.

Yes, please.

> >> Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
> >> ---
> >>  drivers/iommu/arm-smmu.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> >> index 41afb07..2f4a130 100644
> >> --- a/drivers/iommu/arm-smmu.c
> >> +++ b/drivers/iommu/arm-smmu.c
> >> @@ -1405,6 +1405,9 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
> >>       struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
> >>       struct io_pgtable_ops *ops= smmu_domain->pgtbl_ops;
> >>
> >> +     if (domain->type == IOMMU_DOMAIN_IDENTITY)
> >> +             return iova;
> >> +
> >>       if (!ops)
> >>               return 0;
> >
> > I'd have thought ops would be NULL, since arm_smmu_init_domain_context
> > doesn't allocate them for an identity domain.
> Yes ops is set to NULL.

Argh, sorry, I completely overlooked that we return 0 in that case, rather
than the iova.

> > I don't understand this patch. Please can you explain the problem more
> > clearly?
> AFAIK for any driver outside IOMMU there is only one way to identify
> if device is attached to
> IOMMU or not and that is by checking iommu_domain. And I don't think
> it would be appropriate
> for the driver to check domain->type before calling 'iommu_iova_to_phys()' API.
> 
> The difference between IOMMU disabled and IOMMU being in passthrough
> mode is that, in the
> later case device is still attached to default domain but in former's
> case it's NULL. So there is no
> way to differentiate for the external driver whether IOMMU is in
> passthrough mode or DMA mode.
> 
> And since ops is NULL in passthrough mode, 'iommu_iova_to_phys()' will
> return zero.
> 
> Use case for your reference
> https://lkml.org/lkml/2017/3/7/299
> This driver is for a NIC interface on platform which supports SMMUv2.

Blimey, that driver is horrible, but I take your point on the API. Please
repost, fixing SMMUv3 at the same time.

Will

Re: [PATCH] iommu/arm-smmu: Return IOVA in iova_to_phys when SMMU is bypassed

[Sunil Kovvuri]

On Mon, Apr 24, 2017 at 9:30 PM, Will Deacon <will.deacon@arm.com> wrote:
> On Mon, Apr 24, 2017 at 09:23:16PM +0530, Sunil Kovvuri wrote:
>> On Mon, Apr 24, 2017 at 8:14 PM, Will Deacon <will.deacon@arm.com> wrote:
>> > On Mon, Apr 17, 2017 at 05:27:26PM +0530, sunil.kovvuri@gmail.com wrote:
>> >> From: Sunil Goutham <sgoutham@cavium.com>
>> >>
>> >> For software initiated address translation, when domain type is
>> >> IOMMU_DOMAIN_IDENTITY i.e SMMU is bypassed, mimic HW behavior
>> >> i.e return the same IOVA as translated address.
>> >>
>> >> This patch is an extension to Will Deacon's patchset
>> >> "Implement SMMU passthrough using the default domain".
>> >
>> > Are you actually seeing an issue here? If so, why isn't SMMUv3 affected too?
>> Yes and SMMUv3 should also be effected but as of now I don't see any use case.
>> If needed, i can re-submit the patch with changes in SMMUv3 as well.
>
> Yes, please.
>
>> >> Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
>> >> ---
>> >>  drivers/iommu/arm-smmu.c | 3 +++
>> >>  1 file changed, 3 insertions(+)
>> >>
>> >> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> >> index 41afb07..2f4a130 100644
>> >> --- a/drivers/iommu/arm-smmu.c
>> >> +++ b/drivers/iommu/arm-smmu.c
>> >> @@ -1405,6 +1405,9 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
>> >>       struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>> >>       struct io_pgtable_ops *ops= smmu_domain->pgtbl_ops;
>> >>
>> >> +     if (domain->type == IOMMU_DOMAIN_IDENTITY)
>> >> +             return iova;
>> >> +
>> >>       if (!ops)
>> >>               return 0;
>> >
>> > I'd have thought ops would be NULL, since arm_smmu_init_domain_context
>> > doesn't allocate them for an identity domain.
>> Yes ops is set to NULL.
>
> Argh, sorry, I completely overlooked that we return 0 in that case, rather
> than the iova.
>
>> > I don't understand this patch. Please can you explain the problem more
>> > clearly?
>> AFAIK for any driver outside IOMMU there is only one way to identify
>> if device is attached to
>> IOMMU or not and that is by checking iommu_domain. And I don't think
>> it would be appropriate
>> for the driver to check domain->type before calling 'iommu_iova_to_phys()' API.
>>
>> The difference between IOMMU disabled and IOMMU being in passthrough
>> mode is that, in the
>> later case device is still attached to default domain but in former's
>> case it's NULL. So there is no
>> way to differentiate for the external driver whether IOMMU is in
>> passthrough mode or DMA mode.
>>
>> And since ops is NULL in passthrough mode, 'iommu_iova_to_phys()' will
>> return zero.
>>
>> Use case for your reference
>> https://lkml.org/lkml/2017/3/7/299
>> This driver is for a NIC interface on platform which supports SMMUv2.
>
> Blimey, that driver is horrible, but I take your point on the API. Please
> repost, fixing SMMUv3 at the same time.

Sure, will re-submit the patch with SMMUv3 changes.

On a separate note, if you have time, I would definitely like to know
your feedback and what's horrible in that driver, probably in a different
email to keep that out of scope of this patch.

Thanks,
Sunil.