linux-kernel - Re: [PATCH v13 09/13] iommu/sva: Refactoring iommu_sva_bind/unbind

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Message-ID: <682d8922-200d-8c89-7142-83e7b3754b8d@linux.intel.com>
Date:   Wed, 7 Sep 2022 09:27:30 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v13 09/13] iommu/sva: Refactoring
 iommu_sva_bind/unbind_device()

Hi Jean,

On 2022/9/7 0:36, Jean-Philippe Brucker wrote:
> On Tue, Sep 06, 2022 at 08:44:54PM +0800, Lu Baolu wrote:
>> +/**
>> + * iommu_sva_bind_device() - Bind a process address space to a device
>> + * @dev: the device
>> + * @mm: the mm to bind, caller must hold a reference to mm_users
>> + *
>> + * Create a bond between device and address space, allowing the device to access
>> + * the mm using the returned PASID. If a bond already exists between @device and
>> + * @mm, it is returned and an additional reference is taken. Caller must call
>> + * iommu_sva_unbind_device() to release each reference.
> This isn't true anymore. How about storing handle in the domain?

Yes, agreed. How about making the comments like this:

/**
  * iommu_sva_bind_device() - Bind a process address space to a device
  * @dev: the device
  * @mm: the mm to bind, caller must hold a reference to mm_users
  *
  * Create a bond between device and address space, allowing the device to
  * access the mm using the pasid returned by iommu_sva_get_pasid(). If a
  * bond already exists between @device and @mm, an additional internal
  * reference is taken. The reference will be released when the caller calls
  * iommu_sva_unbind_device().

Storing the handle in the domain looks odd. Conceptually an iommu domain
represents a hardware page table and the SVA handle represents a
relationship between device and the page table for a consumer. It's
better to make them separated.

In a separated series, probably we can discuss the possibility of
removing handle from the driver APIs. Just simply return the sva domain
instead.

struct iommu_domain *iommu_sva_bind_device(struct device *dev,
                                            struct mm_struct *mm);
void iommu_sva_unbind_device(struct device *dev,
                              struct iommu_domain *domain);
u32 iommu_sva_get_pasid(struct iommu_domain *domain);

If you think it's appropriate, I can send out the code for discussion.

> 
> (Maybe also drop my Reviewed-by tags since this has changed significantly,
> I tend to ignore patches that have them)

I am sorry that after your review, the SVA domain and attach/detach
device pasid interfaces have undergone some changes. They mainly exist
in the following patches. Can you please help to take a look.

iommu/sva: Refactoring iommu_sva_bind/unbind_device()
arm-smmu-v3/sva: Add SVA domain support
iommu: Add IOMMU SVA domain support
iommu: Add attach/detach_dev_pasid iommu interfaces

Best regards,
baolu