linux-kernel - Re: [PATCH v2 1/2] vfio/iommu_type1: Populate full dirty when detach non-pinned group

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Message-ID: <f8de434c-1993-cfe8-c451-2235be1ceb85@huawei.com>
Date:   Mon, 18 Jan 2021 20:25:09 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <kvmarm@...ts.cs.columbia.edu>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Will Deacon <will@...nel.org>, "Marc Zyngier" <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Mark Rutland" <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        "Robin Murphy" <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Suzuki K Poulose" <suzuki.poulose@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        <wanghaibin.wang@...wei.com>, <jiangkunkun@...wei.com>
Subject: Re: [PATCH v2 1/2] vfio/iommu_type1: Populate full dirty when detach
 non-pinned group



On 2021/1/16 2:01, Alex Williamson wrote:
> On Fri, 15 Jan 2021 17:26:42 +0800
> Keqian Zhu <zhukeqian1@...wei.com> wrote:
> 
>> If a group with non-pinned-page dirty scope is detached with dirty
>> logging enabled, we should fully populate the dirty bitmaps at the
>> time it's removed since we don't know the extent of its previous DMA,
>> nor will the group be present to trigger the full bitmap when the user
>> retrieves the dirty bitmap.
>>
>> Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking")
>> Suggested-by: Alex Williamson <alex.williamson@...hat.com>
>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 18 +++++++++++++++++-
>>  1 file changed, 17 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 0b4dedaa9128..4e82b9a3440f 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -236,6 +236,19 @@ static void vfio_dma_populate_bitmap(struct vfio_dma *dma, size_t pgsize)
>>  	}
>>  }
>>  
>> +static void vfio_iommu_populate_bitmap_full(struct vfio_iommu *iommu)
>> +{
>> +	struct rb_node *n;
>> +	unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
>> +
>> +	for (n = rb_first(&iommu->dma_list); n; n = rb_next(n)) {
>> +		struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
>> +
>> +		if (dma->iommu_mapped)
>> +			bitmap_set(dma->bitmap, 0, dma->size >> pgshift);
>> +	}
>> +}
>> +
>>  static int vfio_dma_bitmap_alloc_all(struct vfio_iommu *iommu, size_t pgsize)
>>  {
>>  	struct rb_node *n;
>> @@ -2415,8 +2428,11 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
>>  	 * Removal of a group without dirty tracking may allow the iommu scope
>>  	 * to be promoted.
>>  	 */
>> -	if (update_dirty_scope)
>> +	if (update_dirty_scope) {
>>  		update_pinned_page_dirty_scope(iommu);
>> +		if (iommu->dirty_page_tracking)
>> +			vfio_iommu_populate_bitmap_full(iommu);
>> +	}
>>  	mutex_unlock(&iommu->lock);
>>  }
>>  
> 
> This doesn't do the right thing.  This marks the bitmap dirty if:
> 
>  * The detached group dirty scope was not limited to pinned pages
> 
>  AND
> 
>  * Dirty tracking is enabled
> 
>  AND
> 
>  * The vfio_dma is *currently* (ie. after the detach) iommu_mapped
> 
> We need to mark the bitmap dirty based on whether the vfio_dma *was*
> iommu_mapped by the group that is now detached.  Thanks,
> 
> Alex
> 
Hi Alex,

Yes, I missed this point again :-(. The update_dirty_scope means we detached
an iommu backed group, and that means the vfio_dma *was* iommu_mapped by this
group, so we can populate full bitmap unconditionally, right?

Thanks,
Keqian


> .
>