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Date:   Mon, 21 Mar 2022 09:50:21 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Lu Baolu <baolu.lu@linux.intel.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Christoph Hellwig <hch@infradead.org>,
        Kevin Tian <kevin.tian@intel.com>,
        Ashok Raj <ashok.raj@intel.com>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Eric Auger <eric.auger@redhat.com>,
        Liu Yi L <yi.l.liu@intel.com>,
        Jacob jun Pan <jacob.jun.pan@intel.com>,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 10/11] iommu: Make IOPF handling framework generic
Message-ID: <20220321125021.GQ11336@nvidia.com>
References: <20220320064030.2936936-1-baolu.lu@linux.intel.com>
 <20220320064030.2936936-11-baolu.lu@linux.intel.com>
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On Sun, Mar 20, 2022 at 02:40:29PM +0800, Lu Baolu wrote:

> +static enum iommu_page_response_code
> +iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
> +{
> +	vm_fault_t ret;
> +	struct mm_struct *mm;
> +	struct vm_area_struct *vma;
> +	unsigned int access_flags = 0;
> +	struct iommu_domain *domain = data;

Why is the iommu_domain not passed in as a fully typed object? I would
think data should some opaque value used by non-sva cases.

What is the lifetime model here anyhow?

> +	unsigned int fault_flags = FAULT_FLAG_REMOTE;
> +	struct iommu_fault_page_request *prm = &fault->prm;
> +	enum iommu_page_response_code status = IOMMU_PAGE_RESP_INVALID;
> +
> +	if (!(prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID))
> +		return status;
> +
> +	mm = domain->sva_cookie;
> +	if (IS_ERR_OR_NULL(mm))

Do not use this function

Do not store err pointers in structs.

> +out_put_mm:
> +	mmap_read_unlock(mm);
> +	mmput(mm);

mm structs are weird, they have two refcounts.

The 'sva_cookie' should hold a mmgrab/mmdrop() refcount to keep the
pointer alive but to touch the mmap lock you have to upgrade it to a
refcount that prevents destruction using mmget_not_zero() just for
this short period.

Jason