linux-kernel - Re: [PATCH 3/6] vfio/iommu_type1: Initially set the pinned_page_dirty

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Date:   Mon, 18 Jan 2021 21:34:36 +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>, 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 3/6] vfio/iommu_type1: Initially set the
 pinned_page_dirty_scope



On 2021/1/16 7:30, Alex Williamson wrote:
> On Thu, 7 Jan 2021 12:43:58 +0800
> Keqian Zhu <zhukeqian1@...wei.com> wrote:
> 
>> For now there are 3 ways to promote the pinned_page_dirty_scope
>> status of vfio_iommu:
>>
>> 1. Through vfio pin interface.
>> 2. Detach a group without pinned_dirty_scope.
>> 3. Attach a group with pinned_dirty_scope.
>>
>> For point 3, the only chance to promote the pinned_page_dirty_scope
>> status is when vfio_iommu is newly created. As we can safely set
>> empty vfio_iommu to be at pinned status, then the point 3 can be
>> removed to reduce operations.
>>
>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 4 +---
>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 110ada24ee91..b596c482487b 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -2045,11 +2045,8 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>>  			 * Non-iommu backed group cannot dirty memory directly,
>>  			 * it can only use interfaces that provide dirty
>>  			 * tracking.
>> -			 * The iommu scope can only be promoted with the
>> -			 * addition of a dirty tracking group.
>>  			 */
>>  			group->pinned_page_dirty_scope = true;
>> -			promote_pinned_page_dirty_scope(iommu);
>>  			mutex_unlock(&iommu->lock);
>>  
>>  			return 0;
>> @@ -2436,6 +2433,7 @@ static void *vfio_iommu_type1_open(unsigned long arg)
>>  	INIT_LIST_HEAD(&iommu->iova_list);
>>  	iommu->dma_list = RB_ROOT;
>>  	iommu->dma_avail = dma_entry_limit;
>> +	iommu->pinned_page_dirty_scope = true;
>>  	mutex_init(&iommu->lock);
>>  	BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
>>  
> 
> This would be resolved automatically if we used the counter approach I
> mentioned on the previous patch, adding a pinned-page scope group simply
> wouldn't increment the iommu counter, which would initially be zero
> indicating no "all-dma" groups.  Thanks,
> 
Sure, I will do that, thanks.

Keqian.

> Alex
> 
> .
>