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Re: [Xen-devel] [PATCH] [IOEMU]: fix the crash of HVM live migration wit

To: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [IOEMU]: fix the crash of HVM live migration with intensive disk access
From: "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
Date: Wed, 12 Aug 2009 11:09:44 +0800
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
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Stefano Stabellini wrote:
On Tue, 11 Aug 2009, Zhai, Edwin wrote:
 [IOEMU]: fix the crash of HVM live migration with intensive disk access

Intensive disk access, e.g. sum of big file, during HVM live migration would cause guest error even file system crash. Guest dmesg said
"attempt to access beyond end of device
hda1: rw=0, want=10232032112, limit=10474317"

Current map cache used by qemu dma doesn't mark the page dirty, so that these pages(probably holding DMA data struct) are not transferred in the last iteration during live migration.

This patch fixes it, and also merges the qemu's original dirty bitmap used by other devices such as vga.

Signed-Off-By: Zhai Edwin <edwin.zhai@xxxxxxxxx>

I think the fix is correct but we should thinking about dropping
logdirty and start using xc_hvm_modified_memory instead for all cases.

One interface should be better. But I'm not sure about the perf implications. You know, qemu use logdirty for its device emulation even without live migration, e.g. vga screen refresh. Changing to xc_hvm_modified_memory would cause many hypercall to set/get the bitmap in xen...

I think Gianluca also may have something to say about this but this week
he is on vacation.

best rgds,

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