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Date: Mon, 20 Jun 2016 11:40:17 -0400
From: Ido Yariv <ido@wizery.com>
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Subject: Re: [Qemu-devel] [PATCH] i386: pci-assign: Fix MSI-X table size
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, Richard Henderson <rth@twiddle.net>, Eduardo Habkost <ehabkost@redhat.com>, Alex Williamson <alex.williamson@redhat.com>

Hi Paolo,

On Mon, Jun 20, 2016 at 04:54:17PM +0200, Paolo Bonzini wrote:
> On 18/06/2016 22:42, Ido Yariv wrote:
> > The current code creates a whole page mmio region for the MSI-X table
> > size.
> > 
> > However, the page containing the MSI-X table may contain other registers
> > not related to MSI-X. Creating an mmio region for the whole page masks
> > such registers and may break drivers in the guest OS.
> > 
> > Since maximal number of entries is known, use that instead to deduce the
> > table size when setting up the mmio region.
> > 
> > Signed-off-by: Ido Yariv <ido@wizery.com>
> 
> I can take this patch, but I'd like to warn you that pci-assign is
> deprecated (and replaced by VFIO).  I seem to recall VFIO does this
> correctly, but it would be great if you could check that.

Just gave it a quick shot and everything seems to be working fine with
VFIO, thanks!

> Also, I would prefer the mmap/munmap to keep using MSIX_PAGE_SIZE, just
> to limit the number of things that could break.

I believe there might be another issue with this. The number of entries
can be up to 2048, so the MSI-X table size can theoretically exceed one
page and take up to 8 pages.

We can just modify MSIX_PAGE_SIZE to 0x8000, but wouldn't it be better
to just map exactly what we need?

Cheers,
Ido.