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

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Message-ID: <20201215085359.053e73ed@x1.home>
Date:   Tue, 15 Dec 2020 08:53:59 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     zhukeqian <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 Tue, 15 Dec 2020 17:37:11 +0800
zhukeqian <zhukeqian1@...wei.com> wrote:

> Hi Alex,
> 
> On 2020/12/15 8:04, Alex Williamson wrote:
> > 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.
> >   
> OK, I will.
> 
> >>
> >> 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,  
> 
> Good spot :-). The code will skip bitmap_set under this situation.
> 
> We should set the bitmap unconditionally when vfio_iommu is promoted,
> as we must have IOMMU backed domain before promoting the vfio_iommu.
> 
> Besides, I think we should also mark dirty in vfio_remove_dma if dirty
> tracking is active. Right?

There's no remaining bitmap to mark dirty if the vfio_dma is removed.
In this case it's the user's responsibility to collect remaining dirty
pages using the VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP support in the
VFIO_IOMMU_UNMAP_DMA ioctl.  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,  
> > 
> > .
> >   
>