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

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Message-ID: <20210115163041.704a4e9d@omen.home.shazbot.org>
Date:   Fri, 15 Jan 2021 16:30:41 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Keqian Zhu <zhukeqian1@...wei.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 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,

Alex