QEMU-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: Yan Zhao <yan.y.zhao@intel.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: "Zhengxiao.zx@Alibaba-inc.com" <Zhengxiao.zx@Alibaba-inc.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	"Liu, Yi L" <yi.l.liu@intel.com>,
	"cjia@nvidia.com" <cjia@nvidia.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"eskultet@redhat.com" <eskultet@redhat.com>,
	"Yang, Ziye" <ziye.yang@intel.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"cohuck@redhat.com" <cohuck@redhat.com>,
	"shuangtai.tst@alibaba-inc.com" <shuangtai.tst@alibaba-inc.com>,
	"dgilbert@redhat.com" <dgilbert@redhat.com>,
	"Wang, Zhi A" <zhi.a.wang@intel.com>,
	"mlevitsk@redhat.com" <mlevitsk@redhat.com>,
	"pasic@linux.ibm.com" <pasic@linux.ibm.com>,
	"aik@ozlabs.ru" <aik@ozlabs.ru>,
	Kirti Wankhede <kwankhede@nvidia.com>,
	"eauger@redhat.com" <eauger@redhat.com>,
	"felipe@nutanix.com" <felipe@nutanix.com>,
	"jonathan.davies@nutanix.com" <jonathan.davies@nutanix.com>,
	"Liu, Changpeng" <changpeng.liu@intel.com>,
	"Ken.Xue@amd.com" <Ken.Xue@amd.com>
Subject: Re: [PATCH v16 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking.
Date: Mon, 30 Mar 2020 20:50:47 -0400
Message-ID: <20200331005046.GB6631@joy-OptiPlex-7040> (raw)
In-Reply-To: <20200330185347.58b1ab93@x1.home>

On Tue, Mar 31, 2020 at 08:53:47AM +0800, Alex Williamson wrote:
> On Mon, 30 Mar 2020 19:51:31 -0400
> Yan Zhao <yan.y.zhao@intel.com> wrote:
> 
> > On Mon, Mar 30, 2020 at 09:49:21PM +0800, Kirti Wankhede wrote:
> > > 
> > > 
> > > On 3/30/2020 8:54 AM, Yan Zhao wrote:  
> > > > On Fri, Mar 27, 2020 at 01:28:13PM +0800, Kirti Wankhede wrote:  
> > > >> Hit send button little early.
> > > >>  
> > > >>   >
> > > >>   > I checked v12, it's not like what I said.
> > > >>   > In v12, bitmaps are generated per vfio_dma, and combination of the
> > > >>   > bitmaps are required in order to generate a big bitmap suiting for dirty
> > > >>   > query. It can cause problem when offset not aligning.
> > > >>   > But what I propose here is to generate an rb tree orthogonal to the tree
> > > >>   > of vfio_dma.
> > > >>   >
> > > >>   > as to CPU cycles saving, I don't think iterating/translating page by page
> > > >>   > would achieve that purpose.
> > > >>   >  
> > > >>
> > > >> Instead of creating one extra rb tree for dirty pages tracking in v10
> > > >> tried to use dma->pfn_list itself, we tried changes in v10, v11 and v12,
> > > >> latest version is evolved version with best possible approach after
> > > >> discussion. Probably, go through v11 as well.
> > > >> https://patchwork.kernel.org/patch/11298335/
> > > >>  
> > > > I'm not sure why all those previous implementations are bound to
> > > > vfio_dma. for vIOMMU on, in most cases, a vfio_dma is only for a page,
> > > > so generating a one-byte bitmap for a single page in each vfio_dma ?
> > > > is it possible to creating one extra rb tree to keep dirty ranges, and
> > > > one fixed length kernel bitmap whose content is generated on query,
> > > > serving as a bouncing buffer for copy_to_user
> > > >   
> > > 
> > > One fixed length? what should be fixed value? then isn't it better to 
> > > fix the size to dma->size?
> > > 
> > > This is also to prevent DoS attack, user space application can query a 
> > > very large range.
> > >   
> > > >>
> > > >> On 3/27/2020 6:00 AM, Yan Zhao wrote:  
> > > >>> On Fri, Mar 27, 2020 at 05:39:01AM +0800, Kirti Wankhede wrote:  
> > > >>>>
> > > >>>>
> > > >>>> On 3/25/2020 7:41 AM, Yan Zhao wrote:  
> > > >>>>> On Wed, Mar 25, 2020 at 05:18:52AM +0800, Kirti Wankhede wrote:  
> > > >>>>>> VFIO_IOMMU_DIRTY_PAGES ioctl performs three operations:
> > > >>>>>> - Start dirty pages tracking while migration is active
> > > >>>>>> - Stop dirty pages tracking.
> > > >>>>>> - Get dirty pages bitmap. Its user space application's responsibility to
> > > >>>>>>      copy content of dirty pages from source to destination during migration.
> > > >>>>>>
> > > >>>>>> To prevent DoS attack, memory for bitmap is allocated per vfio_dma
> > > >>>>>> structure. Bitmap size is calculated considering smallest supported page
> > > >>>>>> size. Bitmap is allocated for all vfio_dmas when dirty logging is enabled
> > > >>>>>>
> > > >>>>>> Bitmap is populated for already pinned pages when bitmap is allocated for
> > > >>>>>> a vfio_dma with the smallest supported page size. Update bitmap from
> > > >>>>>> pinning functions when tracking is enabled. When user application queries
> > > >>>>>> bitmap, check if requested page size is same as page size used to
> > > >>>>>> populated bitmap. If it is equal, copy bitmap, but if not equal, return
> > > >>>>>> error.
> > > >>>>>>
> > > >>>>>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > > >>>>>> Reviewed-by: Neo Jia <cjia@nvidia.com>
> > > >>>>>> ---
> > > >>>>>>     drivers/vfio/vfio_iommu_type1.c | 266 +++++++++++++++++++++++++++++++++++++++-
> > > >>>>>>     1 file changed, 260 insertions(+), 6 deletions(-)
> > > >>>>>>
> > > >>>>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > > >>>>>> index 70aeab921d0f..874a1a7ae925 100644
> > > >>>>>> --- a/drivers/vfio/vfio_iommu_type1.c
> > > >>>>>> +++ b/drivers/vfio/vfio_iommu_type1.c
> > > >>>>>> @@ -71,6 +71,7 @@ struct vfio_iommu {
> > > >>>>>>     	unsigned int		dma_avail;
> > > >>>>>>     	bool			v2;
> > > >>>>>>     	bool			nesting;
> > > >>>>>> +	bool			dirty_page_tracking;
> > > >>>>>>     };
> > > >>>>>>     
> > > >>>>>>     struct vfio_domain {
> > > >>>>>> @@ -91,6 +92,7 @@ struct vfio_dma {
> > > >>>>>>     	bool			lock_cap;	/* capable(CAP_IPC_LOCK) */
> > > >>>>>>     	struct task_struct	*task;
> > > >>>>>>     	struct rb_root		pfn_list;	/* Ex-user pinned pfn list */
> > > >>>>>> +	unsigned long		*bitmap;
> > > >>>>>>     };
> > > >>>>>>     
> > > >>>>>>     struct vfio_group {
> > > >>>>>> @@ -125,7 +127,21 @@ struct vfio_regions {
> > > >>>>>>     #define IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)	\
> > > >>>>>>     					(!list_empty(&iommu->domain_list))
> > > >>>>>>     
> > > >>>>>> +#define DIRTY_BITMAP_BYTES(n)	(ALIGN(n, BITS_PER_TYPE(u64)) / BITS_PER_BYTE)
> > > >>>>>> +
> > > >>>>>> +/*
> > > >>>>>> + * Input argument of number of bits to bitmap_set() is unsigned integer, which
> > > >>>>>> + * further casts to signed integer for unaligned multi-bit operation,
> > > >>>>>> + * __bitmap_set().
> > > >>>>>> + * Then maximum bitmap size supported is 2^31 bits divided by 2^3 bits/byte,
> > > >>>>>> + * that is 2^28 (256 MB) which maps to 2^31 * 2^12 = 2^43 (8TB) on 4K page
> > > >>>>>> + * system.
> > > >>>>>> + */
> > > >>>>>> +#define DIRTY_BITMAP_PAGES_MAX	(uint64_t)(INT_MAX - 1)
> > > >>>>>> +#define DIRTY_BITMAP_SIZE_MAX	 DIRTY_BITMAP_BYTES(DIRTY_BITMAP_PAGES_MAX)
> > > >>>>>> +
> > > >>>>>>     static int put_pfn(unsigned long pfn, int prot);
> > > >>>>>> +static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu);
> > > >>>>>>     
> > > >>>>>>     /*
> > > >>>>>>      * This code handles mapping and unmapping of user data buffers
> > > >>>>>> @@ -175,6 +191,77 @@ static void vfio_unlink_dma(struct vfio_iommu *iommu, struct vfio_dma *old)
> > > >>>>>>     	rb_erase(&old->node, &iommu->dma_list);
> > > >>>>>>     }
> > > >>>>>>     
> > > >>>>>> +
> > > >>>>>> +static int vfio_dma_bitmap_alloc(struct vfio_dma *dma, uint64_t pgsize)
> > > >>>>>> +{
> > > >>>>>> +	uint64_t npages = dma->size / pgsize;
> > > >>>>>> +  
> > > > If pgsize > dma->size, npages = 0.
> > > > wouldn't it cause problem?
> > > >   
> > > 
> > > This patch-set supports bitmap for smallest supported page size, i.e. 
> > > PAGE_SIZE. vfio_dma_do_map() validates dma->size accordingly. So this 
> > > case will not happen.
> > >   
> > as far as I know, qemu/kvm uses 4k as the unit for dirty page tracking.
> > so why smallest iommu page size is used here?
> > wouldn't it cause problem?
> 
> If your concern is that the IOMMU supports sub-4K page sizes, see
> vfio_pgsize_bitmap().  We actually only support PAGE_SIZE as our
> minimum mapping unit, even if the IOMMU supports less, so PAGE_SIZE is
> our lower bound.  Thanks,

if we always uses PAGE_SIZE, why not use PAGE_SIZE directly?
or returning dirty bitmap unit (e.g. 1 << __ffs(vfio_pgsize_bitmap(iommu)))
to QEMU in VFIO_IOMMU_DIRTY_PAGES_FLAG_START, so that qemu can do possible
conversion if it's not the same unit that QEMU uses.

Thanks
Yan


  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24 21:18 Kirti Wankhede
2020-03-25  2:11 ` Yan Zhao
2020-03-26 21:39   ` Kirti Wankhede
2020-03-27  0:30     ` Yan Zhao
2020-03-27  5:07       ` Kirti Wankhede
2020-03-30  2:07         ` Yan Zhao
2020-03-30 20:47           ` Alex Williamson
2020-03-30 23:49             ` Yan Zhao
2020-03-27  5:28       ` Kirti Wankhede
2020-03-30  3:24         ` Yan Zhao
2020-03-30 13:49           ` Kirti Wankhede
2020-03-30 23:51             ` Yan Zhao
2020-03-31  0:53               ` Alex Williamson
2020-03-31  0:50                 ` Yan Zhao [this message]
2020-03-31  1:12                   ` Alex Williamson
2020-03-31  1:16                     ` Yan Zhao
2020-03-31  2:38                       ` Alex Williamson
2020-03-31  2:40                         ` Zhao, Yan Y
2020-03-27 11:57 ` Dr. David Alan Gilbert
2020-03-27 13:57   ` Alex Williamson
2020-03-27 14:09     ` Dr. David Alan Gilbert
  -- strict thread matches above, loose matches on Subject: below --
2020-03-24 19:32 [PATCH v16 Kernel 0/7] KABIs to support migration for VFIO devices Kirti Wankhede
2020-03-24 19:32 ` [PATCH v16 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking Kirti Wankhede
2020-03-24 20:37   ` Alex Williamson
2020-03-24 20:45     ` Alex Williamson
2020-03-24 21:48       ` Kirti Wankhede

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=20200331005046.GB6631@joy-OptiPlex-7040 \
    --to=yan.y.zhao@intel.com \
    --cc=Ken.Xue@amd.com \
    --cc=Zhengxiao.zx@Alibaba-inc.com \
    --cc=aik@ozlabs.ru \
    --cc=alex.williamson@redhat.com \
    --cc=changpeng.liu@intel.com \
    --cc=cjia@nvidia.com \
    --cc=cohuck@redhat.com \
    --cc=dgilbert@redhat.com \
    --cc=eauger@redhat.com \
    --cc=eskultet@redhat.com \
    --cc=felipe@nutanix.com \
    --cc=jonathan.davies@nutanix.com \
    --cc=kevin.tian@intel.com \
    --cc=kvm@vger.kernel.org \
    --cc=kwankhede@nvidia.com \
    --cc=mlevitsk@redhat.com \
    --cc=pasic@linux.ibm.com \
    --cc=qemu-devel@nongnu.org \
    --cc=shuangtai.tst@alibaba-inc.com \
    --cc=yi.l.liu@intel.com \
    --cc=zhi.a.wang@intel.com \
    --cc=ziye.yang@intel.com \
    /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

QEMU-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/qemu-devel/0 qemu-devel/git/0.git
	git clone --mirror https://lore.kernel.org/qemu-devel/1 qemu-devel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 qemu-devel qemu-devel/ https://lore.kernel.org/qemu-devel \
		qemu-devel@nongnu.org
	public-inbox-index qemu-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.nongnu.qemu-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git