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 v12 Kernel 4/7] vfio iommu: Implementation of ioctl to for dirty pages tracking.
Date: Mon, 10 Feb 2020 21:52:51 -0500 [thread overview]
Message-ID: <20200211025251.GB4530@joy-OptiPlex-7040> (raw)
In-Reply-To: <20200210124454.12e0419a@w520.home>
On Tue, Feb 11, 2020 at 03:44:54AM +0800, Alex Williamson wrote:
> On Mon, 10 Feb 2020 04:49:54 -0500
> Yan Zhao <yan.y.zhao@intel.com> wrote:
>
> > On Sat, Feb 08, 2020 at 03:42:31AM +0800, Kirti Wankhede wrote:
> > > VFIO_IOMMU_DIRTY_PAGES ioctl performs three operations:
> > > - Start pinned and unpinned pages tracking while migration is active
> > > - Stop pinned and unpinned dirty pages tracking. This is also used to
> > > stop dirty pages tracking if migration failed or cancelled.
> > > - Get dirty pages bitmap. This ioctl returns bitmap of dirty pages, its
> > > user space application 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 when dirty logging is enabled for those
> > > vfio_dmas whose vpfn list is not empty or whole range is mapped, in
> > > case of pass-through device.
> > >
> > > There could be multiple option as to when bitmap should be populated:
> > > * Polulate bitmap for already pinned pages when bitmap is allocated for
> > > a vfio_dma with the smallest supported page size. Updates bitmap from
> > > page pinning and unpinning functions. 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,
> > > re-populated bitmap according to requested page size and then copy to
> > > user.
> > > Pros: Bitmap gets populated on the fly after dirty tracking has
> > > started.
> > > Cons: If requested page size is different than smallest supported
> > > page size, then bitmap has to be re-populated again, with
> > > additional overhead of allocating bitmap memory again for
> > > re-population of bitmap.
> > >
> > > * Populate bitmap when bitmap is queried by user application.
> > > Pros: Bitmap is populated with requested page size. This eliminates
> > > the need to re-populate bitmap if requested page size is
> > > different than smallest supported pages size.
> > > Cons: There is one time processing time, when bitmap is queried.
> > >
> > > I prefer later option with simple logic and to eliminate over-head of
> > > bitmap repopulation in case of differnt page sizes. Later option is
> > > implemented in this patch.
> > >
> > > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > > Reviewed-by: Neo Jia <cjia@nvidia.com>
> > > ---
> > > drivers/vfio/vfio_iommu_type1.c | 299 ++++++++++++++++++++++++++++++++++++++--
> > > 1 file changed, 287 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > > index d386461e5d11..df358dc1c85b 100644
> > > --- a/drivers/vfio/vfio_iommu_type1.c
> > > +++ b/drivers/vfio/vfio_iommu_type1.c
> [snip]
> > > @@ -830,6 +924,113 @@ static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
> > > return bitmap;
> > > }
> > >
> > > +static int vfio_iova_dirty_bitmap(struct vfio_iommu *iommu, dma_addr_t iova,
> > > + size_t size, uint64_t pgsize,
> > > + unsigned char __user *bitmap)
> > > +{
> > > + struct vfio_dma *dma;
> > > + dma_addr_t i = iova, iova_limit;
> > > + unsigned int bsize, nbits = 0, l = 0;
> > > + unsigned long pgshift = __ffs(pgsize);
> > > +
> > > + while ((dma = vfio_find_dma(iommu, i, pgsize))) {
> > > + int ret, j;
> > > + unsigned int npages = 0, shift = 0;
> > > + unsigned char temp = 0;
> > > +
> > > + /* mark all pages dirty if all pages are pinned and mapped. */
> > > + if (dma->iommu_mapped) {
> > > + iova_limit = min(dma->iova + dma->size, iova + size);
> > > + npages = iova_limit/pgsize;
> > > + bitmap_set(dma->bitmap, 0, npages);
> > for pass-through devices, it's not good to always return all pinned pages as
> > dirty. could it also call vfio_pin_pages to track dirty pages? or any
> > other interface provided to do that?
>
> See patch 7/7. Thanks,
>
hi Alex and Kirti,
for pass-through devices, though patch 7/7 enables the vendor driver to
set dirty pages by calling vfio_pin_pages, however, its overhead is much
higher than the previous way of generating a bitmap directly to user.
And it also requires pass-through device vendor driver to track guest
operations to know when to call vfio_pin_pages.
There are still use cases like a pass-through device is able to track
dirty pages in its hardware buffer, so is there a way for it pass its
dirty bitmap to user?
Thanks
Yan
next prev parent reply other threads:[~2020-02-11 3:02 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-07 19:42 [PATCH v12 Kernel 0/7] KABIs to support migration for VFIO devices Kirti Wankhede
2020-02-07 19:42 ` [PATCH v12 Kernel 1/7] vfio: KABI for migration interface for device state Kirti Wankhede
2020-02-10 17:25 ` Alex Williamson
2020-02-12 20:56 ` Kirti Wankhede
2020-02-14 10:21 ` Cornelia Huck
2020-02-27 8:58 ` Yan Zhao
2020-02-07 19:42 ` [PATCH v12 Kernel 2/7] vfio iommu: Remove atomicity of ref_count of pinned pages Kirti Wankhede
2020-02-07 19:42 ` [PATCH v12 Kernel 3/7] vfio iommu: Add ioctl definition for dirty pages tracking Kirti Wankhede
2020-02-07 19:42 ` [PATCH v12 Kernel 4/7] vfio iommu: Implementation of ioctl to " Kirti Wankhede
2020-02-10 9:49 ` Yan Zhao
2020-02-10 19:44 ` Alex Williamson
2020-02-11 2:52 ` Yan Zhao [this message]
2020-02-11 3:45 ` Alex Williamson
2020-02-11 4:11 ` Yan Zhao
2020-02-10 17:25 ` Alex Williamson
2020-02-12 20:56 ` Kirti Wankhede
2020-02-12 23:13 ` Alex Williamson
2020-02-13 20:11 ` Kirti Wankhede
2020-02-13 23:20 ` Alex Williamson
2020-02-17 19:13 ` Kirti Wankhede
2020-02-17 20:55 ` Alex Williamson
2020-02-18 5:58 ` Kirti Wankhede
2020-02-18 21:41 ` Alex Williamson
2020-02-19 4:21 ` Kirti Wankhede
2020-02-19 4:53 ` Alex Williamson
2020-02-07 19:42 ` [PATCH v12 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap Kirti Wankhede
2020-02-10 17:48 ` Alex Williamson
2020-02-07 19:42 ` [PATCH v12 Kernel 6/7] vfio iommu: Adds flag to indicate dirty pages tracking capability support Kirti Wankhede
2020-02-07 19:42 ` [PATCH v12 Kernel 7/7] vfio: Selective dirty page tracking if IOMMU backed device pins pages Kirti Wankhede
2020-02-10 18:14 ` Alex Williamson
2020-03-09 7:46 ` [PATCH v12 Kernel 0/7] KABIs to support migration for VFIO devices Zengtao (B)
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