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From: Marcel Apfelbaum <marcel.a@redhat.com>
Date: Fri, 08 Nov 2013 17:08:48 +0200
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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: Paolo Bonzini <pbonzini@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>

On Fri, 2013-11-08 at 09:05 +0100, Paolo Bonzini wrote:
> Il 07/11/2013 22:51, Peter Maydell ha scritto:
> >> > 1. Not all architectures have the behavior: "Address space that is not RAM(and friends)
> >> >     is for sure PCI". Only x86 behaves like this (I think).
> > 
> > More specifically, the x86 pc behaves like this. Other
> > x86 based systems could in theory behave differently
> > (not that we actually model any, I think).
> 
> After Marcel's patch, we have changed behavior for at least all boards
> that pass get_system_memory() to pci_register_bus or pci_bus_new:
> 
> * mips/gt64xxx_pci.c
> 
> * pci-host/bonito.c
> 
> * pci-host/ppce500.c
> 
> * ppc/ppc4xx_pci.c
> 
> * sh4/sh_pci.c
> 
> These now will not go anymore through unassigned_mem_ops, which is a
> behavioral change for MIPS boards (gt64xxx_pci and bonito) at least.
> 
> Furthermore, the default behavior of the memory API _is_ read
> all-ones/ignore writes, so I'm not sure what's the benefit of adding a
> separate region for master abort...
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.
This was the main reason I submitted this patch. I had *no* clue that
it would impact so much the system...
I still think the patch is needed ans the guests will benefit from
more accurate PCI spec emulation.

Thanks,
Marcel

> 
> Paolo