linux-kernel - Re: [PATCH] iommu: iommu_group_alloc_default_domain: Fix ops->default

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Date: Thu, 25 Jan 2024 12:56:08 +0200
From: Ovidiu Panait <ovidiu.panait@...driver.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, robin.murphy@....com,
        will@...nel.org, joro@...tes.org
Subject: Re: [PATCH] iommu: iommu_group_alloc_default_domain: Fix
 ops->default_domain codepath

Hi Jason,

On 23.01.2024 19:49, Jason Gunthorpe wrote:
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>
> On Tue, Jan 23, 2024 at 06:58:29PM +0200, ovidiu.panait@...driver.com wrote:
>> From: Ovidiu Panait <ovidiu.panait@...driver.com>
>>
>> Since commit [1], FSL_PAMU initialization on t4240rdb board fails
>> with: "fsl-pamu-domain: pamu_domain_init: Can't register iommu device".
>>
>> Commit [1] changed the behavior for drivers that set ops->default_domain,
>> as the function iommu_group_alloc_default_domain() is now called with
>> "req_type == IOMMU_DOMAIN_IDENTITY", rather than "req_type == 0". This
>> causes the following EINVAL condition to be hit during FSL_PAMU
>> initialization:
>>    ...
>>         if (ops->default_domain) {
>>                 if (req_type)
>>                         return ERR_PTR(-EINVAL);
>>                 return ops->default_domain;
>>         }
>>    ...
>>
>> To avoid this issue when ops->default_domain != NULL, remove the check for
>> non-zero req_type and always return the proper default domain, as set in
>> the driver.
>>
>>    [1] 0f6a90436a57 ("iommu: Do not use IOMMU_DOMAIN_DMA [...]")
>>
>> Fixes: 0f6a90436a57 ("iommu: Do not use IOMMU_DOMAIN_DMA if CONFIG_IOMMU_DMA is not enabled")
>> Signed-off-by: Ovidiu Panait <ovidiu.panait@...driver.com>
>> ---
>>   drivers/iommu/iommu.c | 5 +----
>>   1 file changed, 1 insertion(+), 4 deletions(-)
> Oh, that is a neat combination of things
>
> Removing the test will cause problems for the sys flow - I think the
> right thing is to get the correct req_type earlier. paml wants to use
> a specific domain type so it should not be switching to identity at
> all.
>
> Does the below work for you?
Yes, this works, thanks a lot!
> Also, what is your interest here? I have been wanting to delete this
> driver, would your system still be OK for your usage if it was
> removed?
CONFIG_FSL_PAMU is enabled by default in corenet64_smp_defconfig, and it 
looks
like many platforms are based on this config. I actually noticed this issue
while boot testing the mainline kernel on the t4240rdb board with the 
default
corenet64_smp_defconfig.

In this particular case, the board still boots fine with CONFIG_FSL_PAMU 
disabled,
but I'm not sure how/if removing the PAMU driver will impact other 
platforms.

Ovidiu
> Thanks,
> Jason
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 68e648b5576706..7fa3ccdc3286e6 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1799,7 +1799,7 @@ iommu_group_alloc_default_domain(struct iommu_group *group, int req_type)
>           * domain. Do not use in new drivers.
>           */
>          if (ops->default_domain) {
> -               if (req_type)
> +               if (req_type != ops->default_domain->type)
>                          return ERR_PTR(-EINVAL);
>                  return ops->default_domain;
>          }
> @@ -1871,10 +1871,18 @@ static int iommu_get_def_domain_type(struct iommu_group *group,
>          const struct iommu_ops *ops = dev_iommu_ops(dev);
>          int type;
>
> -       if (!ops->def_domain_type)
> -               return cur_type;
> -
> -       type = ops->def_domain_type(dev);
> +       if (ops->default_domain) {
> +               /*
> +                * Drivers that declare a global static default_domain will
> +                * always choose that.
> +                */
> +               type = ops->default_domain->type;
> +       } else {
> +               if (ops->def_domain_type)
> +                       type = ops->def_domain_type(dev);
> +               else
> +                       type = cur_type;
> +       }
>          if (!type || cur_type == type)
>                  return cur_type;
>          if (!cur_type)