Re: [PATCH] xen/arm: smmuv1: remove iommu group when deassign a device

[Julien Grall <julien@xxxxxxx>]

Hi,

On 27/04/2022 17:15, Rahul Singh wrote:
> When a device is deassigned from the domain it is required to remove the
> iommu group.
This read wrong to me. We should not need to re-create the IOMMU group 
(and call arm_smmu_add_device()) every time a device is re-assigned.
> If we don't remove the group, the next time when we assign
> a device, SME and S2CR will not be setup correctly for the device
> because of that SMMU fault will be observed.
I think this is a bug fix for 0435784cc75dcfef3b5f59c29deb1dbb84265ddb. 
If so, please add a Fixes tag.
> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
> ---
>   xen/drivers/passthrough/arm/smmu.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/xen/drivers/passthrough/arm/smmu.c 
> b/xen/drivers/passthrough/arm/smmu.c
> index 5cacb2dd99..9a31c332d0 100644
> --- a/xen/drivers/passthrough/arm/smmu.c
> +++ b/xen/drivers/passthrough/arm/smmu.c
> @@ -1690,6 +1690,8 @@ static void arm_smmu_detach_dev(struct iommu_domain 
> *domain, struct device *dev)
>         if (cfg)
>                 arm_smmu_master_free_smes(cfg);
>   
> +	iommu_group_put(dev_iommu_group(dev));
> +       dev_iommu_group(dev) = NULL;
>   }
The goal of arm_smmu_detach_dev() is to revert the change made in 
arm_smmu_attach_dev(). But looking at the code, neither the IOMMU group 
nor the smes are allocated in arm_smmu_attach_dev().
Are the SMES meant to be re-allocated everytime we assign to a different 
domain? If yes, the allocation should be done in arm_smmu_attach_dev().
If not, then we should not free the SMES here

IIUC, the SMES have to be re-allocated every time a device is assigned. 
Therefore, I think we should move the call to 
arm_smmu_master_alloc_smes() out of the detach callback and in a helper 
that would be used when removing a device (not yet supported by Xen).
Cheers,

--
Julien Grall