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Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO B
From: |
Rusty Russell |
Subject: |
Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR |
Date: |
Wed, 02 Nov 2011 13:52:55 +1030 |
User-agent: |
Notmuch/0.6.1-1 (http://notmuchmail.org) Emacs/23.3.1 (i686-pc-linux-gnu) |
On Tue, 01 Nov 2011 17:20:06 -0500, Anthony Liguori <address@hidden> wrote:
> On 09/30/2011 12:26 AM, David Gibson wrote:
> > Currently, virtio devices are usually presented to the guest as an
> > emulated PCI device, virtio_pci. Although the actual IO operations
> > are done through system memory, the configuration of the virtio device
> > is done through the one PCI IO space BAR that virtio_pci presents.
> >
> > But PCI IO space (aka PIO) is deprecated for modern PCI devices, and
> > on some systems with many PCI domains accessing PIO space can be
> > problematic. For example on the existing PowerVM implementation of
> > the PAPR spec, PCI PIO access is not supported at all. We're hoping
> > that our KVM implementation will support PCI PIO (once we support PCI
> > at all), but it will probably have some irritating limitations.
> >
> > This patch, therefore, extends the virtio_pci device to have a PCI
> > memory space (MMIO) BAR as well as the IO BAR. The MMIO BAR contains
> > exactly the same registers, in exactly the same layout as the existing
> > PIO BAR.
> >
> > Because the PIO BAR is still present, existing guest drivers should
> > still work fine. With this change in place, future guest drivers can
> > check for an MMIO BAR and use that if present (falling back to PIO
> > when possible to support older qemu versions).
> >
> > Signed-off-by: David Gibson<address@hidden>
>
> Seems harmless for QEMU, so applied. You should update the virtio-pci spec
> too.
>
> Regards,
Can you revert this? We just reverted the kernel part, figuring we need
a rethink.
Thanks,
Rusty.
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Anthony Liguori, 2011/11/01
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, David Gibson, 2011/11/01
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR,
Rusty Russell <=
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Avi Kivity, 2011/11/03
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Anthony Liguori, 2011/11/03
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Avi Kivity, 2011/11/03
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Anthony Liguori, 2011/11/03
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Avi Kivity, 2011/11/03
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Anthony Liguori, 2011/11/03
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Michael S. Tsirkin, 2011/11/03
- Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR, Anthony Liguori, 2011/11/03