kvm.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Kirti Wankhede <kwankhede@nvidia.com>
To: Alex Williamson <alex.williamson@redhat.com>,
	Keqian Zhu <zhukeqian1@huawei.com>
Cc: <linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<iommu@lists.linux-foundation.org>, <kvm@vger.kernel.org>,
	<kvmarm@lists.cs.columbia.edu>, Cornelia Huck <cohuck@redhat.com>,
	"Will Deacon" <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	James Morse <james.morse@arm.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Joerg Roedel <joro@8bytes.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexios Zavras <alexios.zavras@intel.com>,
	<wanghaibin.wang@huawei.com>, <jiangkunkun@huawei.com>
Subject: Re: [PATCH 1/5] vfio/iommu_type1: Fixes vfio_dma_populate_bitmap to avoid dirty lose
Date: Wed, 13 Jan 2021 18:05:43 +0530	[thread overview]
Message-ID: <3f4f9a82-0934-b114-8bd8-452e9e56712f@nvidia.com> (raw)
In-Reply-To: <20210112142059.074c1b0f@omen.home.shazbot.org>



On 1/13/2021 2:50 AM, Alex Williamson wrote:
> On Thu, 7 Jan 2021 17:28:57 +0800
> Keqian Zhu <zhukeqian1@huawei.com> wrote:
> 
>> Defer checking whether vfio_dma is of fully-dirty in update_user_bitmap
>> is easy to lose dirty log. For example, after promoting pinned_scope of
>> vfio_iommu, vfio_dma is not considered as fully-dirty, then we may lose
>> dirty log that occurs before vfio_iommu is promoted.
>>
>> The key point is that pinned-dirty is not a real dirty tracking way, it
>> can't continuously track dirty pages, but just restrict dirty scope. It
>> is essentially the same as fully-dirty. Fully-dirty is of full-scope and
>> pinned-dirty is of pinned-scope.
>>
>> So we must mark pinned-dirty or fully-dirty after we start dirty tracking
>> or clear dirty bitmap, to ensure that dirty log is marked right away.
> 
> I was initially convinced by these first three patches, but upon
> further review, I think the premise is wrong.  AIUI, the concern across
> these patches is that our dirty bitmap is only populated with pages
> dirtied by pinning and we only take into account the pinned page dirty
> scope at the time the bitmap is retrieved by the user.  You suppose
> this presents a gap where if a vendor driver has not yet identified
> with a page pinning scope that the entire bitmap should be considered
> dirty regardless of whether that driver later pins pages prior to the
> user retrieving the dirty bitmap.
> 
> I don't think this is how we intended the cooperation between the iommu
> driver and vendor driver to work.  By pinning pages a vendor driver is
> not declaring that only their future dirty page scope is limited to
> pinned pages, instead they're declaring themselves as a participant in
> dirty page tracking and take responsibility for pinning any necessary
> pages.  For example we might extend VFIO_IOMMU_DIRTY_PAGES_FLAG_START
> to trigger a blocking notification to groups to not only begin dirty
> tracking, but also to synchronously register their current device DMA
> footprint.  This patch would require a vendor driver to possibly perform
> a gratuitous page pinning in order to set the scope prior to dirty
> logging being enabled, or else the initial bitmap will be fully dirty.
> 
> Therefore, I don't see that this series is necessary or correct.  Kirti,
> does this match your thinking?
> 

That's correct Alex and I agree with you.

> Thinking about these semantics, it seems there might still be an issue
> if a group with non-pinned-page dirty scope is detached with dirty
> logging enabled.  

Hot-unplug a device while migration process has started - is this 
scenario supported?

Thanks,
Kirti

> It seems this should in fact 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.  Creating fully populated
> bitmaps at the time tracking is enabled negates our ability to take
> advantage of later enlightenment though.  Thanks,
> 
> Alex
> 
>> Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking")
>> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
>> ---
>>   drivers/vfio/vfio_iommu_type1.c | 33 ++++++++++++++++++++++-----------
>>   1 file changed, 22 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index bceda5e8baaa..b0a26e8e0adf 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -224,7 +224,7 @@ static void vfio_dma_bitmap_free(struct vfio_dma *dma)
>>   	dma->bitmap = NULL;
>>   }
>>   
>> -static void vfio_dma_populate_bitmap(struct vfio_dma *dma, size_t pgsize)
>> +static void vfio_dma_populate_bitmap_pinned(struct vfio_dma *dma, size_t pgsize)
>>   {
>>   	struct rb_node *p;
>>   	unsigned long pgshift = __ffs(pgsize);
>> @@ -236,6 +236,25 @@ static void vfio_dma_populate_bitmap(struct vfio_dma *dma, size_t pgsize)
>>   	}
>>   }
>>   
>> +static void vfio_dma_populate_bitmap_full(struct vfio_dma *dma, size_t pgsize)
>> +{
>> +	unsigned long pgshift = __ffs(pgsize);
>> +	unsigned long nbits = dma->size >> pgshift;
>> +
>> +	bitmap_set(dma->bitmap, 0, nbits);
>> +}
>> +
>> +static void vfio_dma_populate_bitmap(struct vfio_iommu *iommu,
>> +				     struct vfio_dma *dma)
>> +{
>> +	size_t pgsize = (size_t)1 << __ffs(iommu->pgsize_bitmap);
>> +
>> +	if (iommu->pinned_page_dirty_scope)
>> +		vfio_dma_populate_bitmap_pinned(dma, pgsize);
>> +	else if (dma->iommu_mapped)
>> +		vfio_dma_populate_bitmap_full(dma, pgsize);
>> +}
>> +
>>   static int vfio_dma_bitmap_alloc_all(struct vfio_iommu *iommu)
>>   {
>>   	struct rb_node *n;
>> @@ -257,7 +276,7 @@ static int vfio_dma_bitmap_alloc_all(struct vfio_iommu *iommu)
>>   			}
>>   			return ret;
>>   		}
>> -		vfio_dma_populate_bitmap(dma, pgsize);
>> +		vfio_dma_populate_bitmap(iommu, dma);
>>   	}
>>   	return 0;
>>   }
>> @@ -987,13 +1006,6 @@ static int update_user_bitmap(u64 __user *bitmap, struct vfio_iommu *iommu,
>>   	unsigned long shift = bit_offset % BITS_PER_LONG;
>>   	unsigned long leftover;
>>   
>> -	/*
>> -	 * mark all pages dirty if any IOMMU capable device is not able
>> -	 * to report dirty pages and all pages are pinned and mapped.
>> -	 */
>> -	if (!iommu->pinned_page_dirty_scope && dma->iommu_mapped)
>> -		bitmap_set(dma->bitmap, 0, nbits);
>> -
>>   	if (shift) {
>>   		bitmap_shift_left(dma->bitmap, dma->bitmap, shift,
>>   				  nbits + shift);
>> @@ -1019,7 +1031,6 @@ static int vfio_iova_dirty_bitmap(u64 __user *bitmap, struct vfio_iommu *iommu,
>>   	struct vfio_dma *dma;
>>   	struct rb_node *n;
>>   	unsigned long pgshift = __ffs(iommu->pgsize_bitmap);
>> -	size_t pgsize = (size_t)1 << pgshift;
>>   	int ret;
>>   
>>   	/*
>> @@ -1055,7 +1066,7 @@ static int vfio_iova_dirty_bitmap(u64 __user *bitmap, struct vfio_iommu *iommu,
>>   		 * pages which are marked dirty by vfio_dma_rw()
>>   		 */
>>   		bitmap_clear(dma->bitmap, 0, dma->size >> pgshift);
>> -		vfio_dma_populate_bitmap(dma, pgsize);
>> +		vfio_dma_populate_bitmap(iommu, dma);
>>   	}
>>   	return 0;
>>   }
> 

  reply	other threads:[~2021-01-13 12:37 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-07  9:28 [PATCH 0/5] vfio/iommu_type1: Some fixes about dirty tracking Keqian Zhu
2021-01-07  9:28 ` [PATCH 1/5] vfio/iommu_type1: Fixes vfio_dma_populate_bitmap to avoid dirty lose Keqian Zhu
2021-01-12 21:20   ` Alex Williamson
2021-01-13 12:35     ` Kirti Wankhede [this message]
2021-01-13 15:13       ` Alex Williamson
2021-01-14 13:05     ` Keqian Zhu
2021-01-14 17:14       ` Alex Williamson
2021-01-15  9:41         ` Keqian Zhu
2021-01-07  9:28 ` [PATCH 2/5] vfio/iommu_type1: Populate dirty bitmap for new vfio_dma Keqian Zhu
2021-01-07  9:28 ` [PATCH 3/5] vfio/iommu_type1: Populate dirty bitmap when attach group Keqian Zhu
2021-01-07  9:29 ` [PATCH 4/5] vfio/iommu_type1: Carefully use unmap_unpin_all during dirty tracking Keqian Zhu
2021-01-11 21:49   ` Alex Williamson
2021-01-12 12:04     ` Keqian Zhu
2021-01-12 19:53       ` Alex Williamson
2021-01-14 12:11         ` Keqian Zhu
2021-01-07  9:29 ` [PATCH 5/5] vfio/iommu_type1: Move sanity_check_pfn_list to unmap_unpin_all Keqian Zhu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=3f4f9a82-0934-b114-8bd8-452e9e56712f@nvidia.com \
    --to=kwankhede@nvidia.com \
    --cc=akpm@linux-foundation.org \
    --cc=alex.williamson@redhat.com \
    --cc=alexios.zavras@intel.com \
    --cc=catalin.marinas@arm.com \
    --cc=cohuck@redhat.com \
    --cc=daniel.lezcano@linaro.org \
    --cc=iommu@lists.linux-foundation.org \
    --cc=james.morse@arm.com \
    --cc=jiangkunkun@huawei.com \
    --cc=joro@8bytes.org \
    --cc=julien.thierry.kdev@gmail.com \
    --cc=kvm@vger.kernel.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=maz@kernel.org \
    --cc=robin.murphy@arm.com \
    --cc=suzuki.poulose@arm.com \
    --cc=tglx@linutronix.de \
    --cc=wanghaibin.wang@huawei.com \
    --cc=will@kernel.org \
    --cc=zhukeqian1@huawei.com \
    --subject='Re: [PATCH 1/5] vfio/iommu_type1: Fixes vfio_dma_populate_bitmap to avoid dirty lose' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).