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Date: Thu, 26 Jan 2012 16:05:43 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [RFC/PATCH] Fix guest OS panic when 64bit BAR is
 present
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To: Avi Kivity <avi@redhat.com>
Cc: Alexey Korolev <alexey.korolev@endace.com>, sfd@endace.com, Alex Williamson <alex.williamson@redhat.com>, Kevin O'Connor <kevin@koconnor.net>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

On Thu, Jan 26, 2012 at 03:51:06PM +0200, Avi Kivity wrote:
> > Please look at HPET lines. HPET is mapped to 0xfed00000.
> > Size of ivshmem is 32MB. During pci enumeration ivshmem will corrupt the range from 0xfe000000 - 0xffffffff.
> > It overlaps HPET memory. When Linux does late_hpet init, it finds garbage and this is causing panic.
> >
> 
> Let me see if I get this right: during BAR sizing, the guest sets the
> BAR to ~1, which means 4GB-32MB -> 4GB, which overlaps the HPET.  If so,
> that's expected behaviour.

Yes BAR sizing temporarily sets the BAR to an invalid value then
restores it.  What I don't understand is how come something accesses the
HPET range in between.

> If the guest doesn't want this memory there,
> it should disable mmio.

Recent kernels do this for most devices, but not for
platform devices.

> -- 
> error compiling committee.c: too many arguments to function