From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Jones <drjones@redhat.com>
Subject: Re: [Qemu-devel] [RFC/RFT PATCH v2 0/3] KVM: Introduce
 KVM_MEM_UNCACHED
Date: Thu, 14 May 2015 15:00:37 +0200
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, Marc Zyngier <marc.zyngier@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>, Laszlo Ersek <lersek@redhat.com>, "kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>
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On Thu, May 14, 2015 at 01:38:11PM +0100, Peter Maydell wrote:
> On 14 May 2015 at 13:28, Paolo Bonzini <pbonzini@redhat.com> 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