linux-kernel - Re: [PATCH 4/7] vfio: iommu_type1: Fix missing dirty page when promote pinned

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Message-ID: <20201214170459.50cb8729@omen.home>
Date:   Mon, 14 Dec 2020 17:04:59 -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>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Mark Brown <broonie@...nel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexios Zavras <alexios.zavras@...el.com>,
        <wanghaibin.wang@...wei.com>, <jiangkunkun@...wei.com>
Subject: Re: [PATCH 4/7] vfio: iommu_type1: Fix missing dirty page when
 promote pinned_scope

On Thu, 10 Dec 2020 15:34:22 +0800
Keqian Zhu <zhukeqian1@...wei.com> wrote:

> When we pin or detach a group which is not dirty tracking capable,
> we will try to promote pinned_scope of vfio_iommu.
> 
> If we succeed to do so, vfio only report pinned_scope as dirty to
> userspace next time, but these memory written before pin or detach
> is missed.
> 
> The solution is that we must populate all dma range as dirty before
> promoting pinned_scope of vfio_iommu.

Please don't bury fixes patches into a series with other optimizations
and semantic changes.  Send it separately.

> 
> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index bd9a94590ebc..00684597b098 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -1633,6 +1633,20 @@ static struct vfio_group *vfio_iommu_find_iommu_group(struct vfio_iommu *iommu,
>  	return group;
>  }
>  
> +static void vfio_populate_bitmap_all(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);
> +		unsigned long nbits = dma->size >> pgshift;
> +
> +		if (dma->iommu_mapped)
> +			bitmap_set(dma->bitmap, 0, nbits);
> +	}
> +}


If we detach a group which results in only non-IOMMU backed mdevs,
don't we also clear dma->iommu_mapped as part of vfio_unmap_unpin()
such that this test is invalid?  Thanks,

Alex

> +
>  static void promote_pinned_page_dirty_scope(struct vfio_iommu *iommu)
>  {
>  	struct vfio_domain *domain;
> @@ -1657,6 +1671,10 @@ static void promote_pinned_page_dirty_scope(struct vfio_iommu *iommu)
>  	}
>  
>  	iommu->pinned_page_dirty_scope = true;
> +
> +	/* Set all bitmap to avoid missing dirty page */
> +	if (iommu->dirty_page_tracking)
> +		vfio_populate_bitmap_all(iommu);
>  }
>  
>  static bool vfio_iommu_has_sw_msi(struct list_head *group_resv_regions,