Re: [PATCH 5/5] iommu/arm-smmu-v3: Enforce dirty tracking in domain attach/alloc

From: Joao Martins <joao.m.martins@oracle.com>
To: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Cc: robin.murphy@arm.com, will@kernel.org, joro@8bytes.org,
	jgg@nvidia.com, kevin.tian@intel.com, nicolinc@nvidia.com,
	mshavit@google.com, eric.auger@redhat.com,
	jiangkunkun@huawei.com, zhukeqian1@huawei.com,
	linuxarm@huawei.com, iommu@lists.linux.dev,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 5/5] iommu/arm-smmu-v3: Enforce dirty tracking in domain attach/alloc
Date: Thu, 14 Dec 2023 16:29:03 +0000	[thread overview]
Message-ID: <b2911a1a-9dc1-477c-b003-cb078563f08e@oracle.com> (raw)
In-Reply-To: <20231128094940.1344-6-shameerali.kolothum.thodi@huawei.com>

On 28/11/2023 09:49, Shameer Kolothum wrote:
> From: Joao Martins <joao.m.martins@oracle.com>
> 
> SMMUv3 implements all requirements of revoking device
> attachment if smmu does not support dirty tracking.
> 
> Finally handle the IOMMU_CAP_DIRTY in iommu_capable for
> IOMMUFD_DEVICE_GET_HW_INFO.
> 
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 22 ++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index c5eabdc29ba5..2c100f2136bc 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2244,6 +2244,8 @@ static bool arm_smmu_capable(struct device *dev, enum iommu_cap cap)
>  	case IOMMU_CAP_NOEXEC:
>  	case IOMMU_CAP_DEFERRED_FLUSH:
>  		return true;
> +	case IOMMU_CAP_DIRTY_TRACKING:
> +		return arm_smmu_dbm_capable(master->smmu);
>  	default:
>  		return false;
>  	}
> @@ -2701,6 +2703,9 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>  	master = dev_iommu_priv_get(dev);
>  	smmu = master->smmu;
>  
> +	if (domain->dirty_ops && !arm_smmu_dbm_capable(smmu))
> +		return -EINVAL;
> +
>  	mutex_lock(&smmu_domain->init_mutex);
>  
>  	if (!smmu_domain->smmu) {
> @@ -3077,7 +3082,9 @@ arm_smmu_domain_alloc_user(struct device *dev, u32 flags,
>  			   const struct iommu_user_data *user_data)
>  {
>  	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> -	const u32 paging_flags = IOMMU_HWPT_ALLOC_NEST_PARENT;
> +	const u32 paging_flags = IOMMU_HWPT_ALLOC_NEST_PARENT |
> +				 IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
> +	bool enforce_dirty = flags & IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
>  	struct arm_smmu_domain *smmu_domain;
>  	int ret;
>  
> @@ -3090,6 +3097,10 @@ arm_smmu_domain_alloc_user(struct device *dev, u32 flags,
>  	if (user_data)
>  		return ERR_PTR(-EINVAL);
>  
> +	if (enforce_dirty &&
> +	    !device_iommu_capable(dev, IOMMU_CAP_DIRTY_TRACKING))
> +		return ERR_PTR(-EOPNOTSUPP);
> +
>  	smmu_domain = arm_smmu_domain_alloc();
>  	if (!smmu_domain)
>  		return ERR_PTR(-ENOMEM);
> @@ -3104,6 +3115,9 @@ arm_smmu_domain_alloc_user(struct device *dev, u32 flags,
>  
>  	smmu_domain->domain.type = IOMMU_DOMAIN_UNMANAGED;
>  	smmu_domain->domain.ops = arm_smmu_ops.default_domain_ops;
> +	if (enforce_dirty)
> +		smmu_domain->domain.dirty_ops = &arm_smmu_dirty_ops;
> +
>  	ret = arm_smmu_domain_finalise(smmu_domain, master->smmu);
>  	if (ret)
>  		goto err_free;

Perhaps it would be better to limit the blast radius of the always-on mode, to
just enable it in the context descriptor depending on passing the
HWPT_ALLOC_DIRTY_TRACKING flag instead of enabling for everybody.
Something like this in arm_smmu_domain_finalise():

	if (arm_smmu_dbm_capable(smmu) && smmu_domain->domain.dirty_ops &&
	    smmu_domain->stage == ARM_SMMU_DOMAIN_S1)
		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_ARM_HD;

For bisectability perhaps the second patch of this series should be the last,
while bringing the implementation of arm_smmu_dbm_capable() to this patch.

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