Re: [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking

From: Yang Zhang <yang.zhang.wz@gmail.com>
To: Alexander Duyck <aduyck@mirantis.com>,
	kvm@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org, alexander.duyck@gmail.com,
	qemu-devel@nongnu.org
Cc: tianyu.lan@intel.com, mst@redhat.com, konrad.wilk@oracle.com,
	dgilbert@redhat.com, agraf@suse.de, alex.williamson@redhat.com
Subject: Re: [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking
Date: Mon, 14 Dec 2015 10:27:35 +0800	[thread overview]
Message-ID: <566E2917.7050705@gmail.com> (raw)
In-Reply-To: <20151213212557.5410.48577.stgit@localhost.localdomain>

On 2015/12/14 5:28, Alexander Duyck wrote:
> This patch set is meant to be the guest side code for a proof of concept
> involving leaving pass-through devices in the guest during the warm-up
> phase of guest live migration.  In order to accomplish this I have added a
> new function called dma_mark_dirty that will mark the pages associated with
> the DMA transaction as dirty in the case of either an unmap or a
> sync_.*_for_cpu where the DMA direction is either DMA_FROM_DEVICE or
> DMA_BIDIRECTIONAL.  The pass-through device must still be removed before
> the stop-and-copy phase, however allowing the device to be present should
> significantly improve the performance of the guest during the warm-up
> period.
>
> This current implementation is very preliminary and there are number of
> items still missing.  Specifically in order to make this a more complete
> solution we need to support:
> 1.  Notifying hypervisor that drivers are dirtying DMA pages received
> 2.  Bypassing page dirtying when it is not needed.
>

Shouldn't current log dirty mechanism already cover them?

> The two mechanisms referenced above would likely require coordination with
> QEMU and as such are open to discussion.  I haven't attempted to address
> them as I am not sure there is a consensus as of yet.  My personal
> preference would be to add a vendor-specific configuration block to the
> emulated pci-bridge interfaces created by QEMU that would allow us to
> essentially extend shpc to support guest live migration with pass-through
> devices.
>
> The functionality in this patch set is currently disabled by default.  To
> enable it you can select "SWIOTLB page dirtying" from the "Processor type
> and features" menu.

Only SWIOTLB is supported?

>
> ---
>
> Alexander Duyck (3):
>        swiotlb: Fold static unmap and sync calls into calling functions
>        xen/swiotlb: Fold static unmap and sync calls into calling functions
>        x86: Create dma_mark_dirty to dirty pages used for DMA by VM guest
>
>
>   arch/arm/include/asm/dma-mapping.h       |    3 +
>   arch/arm64/include/asm/dma-mapping.h     |    5 +-
>   arch/ia64/include/asm/dma.h              |    1
>   arch/mips/include/asm/dma-mapping.h      |    1
>   arch/powerpc/include/asm/swiotlb.h       |    1
>   arch/tile/include/asm/dma-mapping.h      |    1
>   arch/unicore32/include/asm/dma-mapping.h |    1
>   arch/x86/Kconfig                         |   11 ++++
>   arch/x86/include/asm/swiotlb.h           |   26 ++++++++
>   drivers/xen/swiotlb-xen.c                |   92 +++++++++++++-----------------
>   lib/swiotlb.c                            |   83 ++++++++++++---------------
>   11 files changed, 123 insertions(+), 102 deletions(-)
>
> --
>

-- 
best regards
yang