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Date: Fri, 08 Nov 2013 17:12:18 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] exec: fix regression by making
 system-memory region UINT64_MAX size
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To: Marcel Apfelbaum <marcel.a@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, "Michael S. Tsirkin" <mst@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>, "edk2-devel@lists.sourceforge.net" <edk2-devel@lists.sourceforge.net>, qemu-devel <qemu-devel@nongnu.org>, Laszlo Ersek <lersek@redhat.com>, Anthony Liguori <anthony@codemonkey.ws>, Jordan Justen <jljusten@gmail.com>, afaerber <afaerber@suse.de>, Richard Henderson <rth@twiddle.net>

Il 08/11/2013 16:08, Marcel Apfelbaum ha scritto:
> Actually, as I see, the default behavior of "system" memory region
> is to use unassigned_mem_ops that has valid.accepts method returning
> false (no read/write methods). I don't see that read all-ones/ignore
> writes is implemented.

Right, it's read-all-zeroes (see unassigned_mem_read).  It was
read-all-ones for a brief time, then it got changed back to read-all-zeroes.

> This was the main reason I submitted this patch. I had *no* clue that
> it would impact so much the system...

Yeah, it's not your fault.  But it should have been held back until 1.8.
 Do you agree with reverting it?

> I still think the patch is needed ans the guests will benefit from
> more accurate PCI spec emulation.

Only buggy guests :) but yes, I agree it's a good thing to have.

Paolo