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

[Andrew Jones]

On Thu, May 14, 2015 at 01:38:11PM +0100, Peter Maydell wrote:
> On 14 May 2015 at 13:28, Paolo Bonzini <address@hidden> wrote:
> > Well, PCI BARs are generally MMIO resources, and hence should not be cached.
> >
> > As an optimization, OS drivers can mark them as cacheable or
> > write-combining or something like that, but in general it's a safe
> > default to leave them uncached---one would think.
> 
> Isn't this handled by the OS mapping them in the 'prefetchable'
> MMIO window rather than the 'non-prefetchable' one? (QEMU's
> generic-PCIe device doesn't yet support the prefetchable window.)

I was thinking (with my limited PCI knowledge) the same thing, and
was planning on experimenting with that.

drew