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Re: [Qemu-devel] [RFC/RFT PATCH v2 0/3] KVM: Introduce KVM_MEM_UNCACHED

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [RFC/RFT PATCH v2 0/3] KVM: Introduce KVM_MEM_UNCACHED
Date: Thu, 14 May 2015 14:08:49 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 14/05/2015 14:00, Christoffer Dall wrote:
> So, getting back to my original question.  Is the point then that UEFI
> must assume (from ACPI/DT) the cache-coherency properties of the PCI
> controller which exists in hardware on the system you're running on,
> even for the virtual PCI bus because that will be the semantics for
> assigned devices?
> And in that case, we have no way to distinguish between passthrough
> devices and virtual devices plugged into the virtual PCI bus?

Well, we could use the subsystem id.  But it's a hack, and may cause
incompatibilities with some drivers.  Michael, any ideas?

> What about the idea of having two virtual PCI buses on your system where
> one is always cache-coherent and uses for virtual devices, and the other
> is whatever the hardware is and used for passthrough devices?

I think that was rejected before.


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