linux-kernel - Re: [PATCH v2 04/11] iommu/arm-smmu-v3: Split block descriptor when start dirty log

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Date:   Tue, 16 Mar 2021 17:17:51 +0800
From:   Yi Sun <yi.y.sun@...ux.intel.com>
To:     Keqian Zhu <zhukeqian1@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org,
        Alex Williamson <alex.williamson@...hat.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        wanghaibin.wang@...wei.com, jiangkunkun@...wei.com,
        yuzenghui@...wei.com, lushenming@...wei.com
Subject: Re: [PATCH v2 04/11] iommu/arm-smmu-v3: Split block descriptor when
 start dirty log

On 21-03-10 17:06:07, Keqian Zhu wrote:
> From: jiangkunkun <jiangkunkun@...wei.com>
> 
> Block descriptor is not a proper granule for dirty log tracking.
> Take an extreme example, if DMA writes one byte, under 1G mapping,
> the dirty amount reported to userspace is 1G, but under 4K mapping,
> the dirty amount is just 4K.
> 
> This adds a new interface named start_dirty_log in iommu layer and
> arm smmuv3 implements it, which splits block descriptor to an span
> of page descriptors. Other types of IOMMU will perform architecture
> specific actions to start dirty log.
> 
> To allow code reuse, the split_block operation is realized as an
> iommu_ops too. We flush all iotlbs after the whole procedure is
> completed to ease the pressure of iommu, as we will hanle a huge
> range of mapping in general.
> 
> Spliting block does not simultaneously work with other pgtable ops,
> as the only designed user is vfio, which always hold a lock, so race
> condition is not considered in the pgtable ops.
> 
> Co-developed-by: Keqian Zhu <zhukeqian1@...wei.com>
> Signed-off-by: Kunkun Jiang <jiangkunkun@...wei.com>
> ---
> 
> changelog:
> 
> v2:
>  - Change the return type of split_block(). size_t -> int.
>  - Change commit message to properly describe race condition. (Robin)
>  - Change commit message to properly describe the need of split block.
>  - Add a new interface named start_dirty_log(). (Sun Yi)
>  - Change commit message to explain the realtionship of split_block() and start_dirty_log().
> 
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c |  52 +++++++++
>  drivers/iommu/io-pgtable-arm.c              | 122 ++++++++++++++++++++
>  drivers/iommu/iommu.c                       |  48 ++++++++
>  include/linux/io-pgtable.h                  |   2 +
>  include/linux/iommu.h                       |  24 ++++
>  5 files changed, 248 insertions(+)
> 
Could you please split iommu common interface to a separate patch?
This may make review and comments easier.

IMHO, I think the start/stop interfaces could be merged into one, e.g:
    int iommu_domain_set_hwdbm(struct iommu_domain *domain, bool enable,
                               unsigned long iova, size_t size,
                               int prot);

Same comments to patch 5.

BRs,
Yi Sun

> -- 
> 2.19.1