Re: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 22/10/2009 03:42, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:

>> This should be written by dom0(likely to be Qemu).  And if it does
>> exist, we may have to prohibit such unsafe writings about MSI in
>> Qemu.  
> 
> Another issue may exist which leads to the issue.  Currenlty, both Qemu and
> hypervisor can program MSI but Xen lacks synchronization mechnism between them
> to avoid race.  As said in the last mail,  Qemu shouldn't be allowed to do the
> unsafe writing about MSI Info, and insteadly,  it should resort to hypervisor
> through hypercall for MSI programing, otherwise, Qemu may write staled MSI
> info to PCI devices  and leads to the strange issues.
> Keir/Ian
> What's your opinion about the potential issue ?  Maybe we need to add a lock
> between them or just allow hypervisor to do the writing ?

In general, having qemu make pci updates via the cf8/cfc method is clearly
unsafe, and cannot be made safe. I would certainly be happy to see some of
the low-level PCI management pushed into pciback (and/or pci-stub, depending
on whether pciback is to be ported to pv_ops).

 -- Keir



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