Re: [Qemu-devel] [PATCH] exec: fix regression by making system-memory region UINT64_MAX size

[Marcel Apfelbaum]

On Fri, 2013-11-08 at 10:44 +0000, Peter Maydell wrote:
> On 8 November 2013 08:05, Paolo Bonzini <address@hidden> 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
> 
> Oh, right. Ideally those boards should not do that (I fixed
> the versatile pci controller not to do that a while back) but
> it's a long standing behaviour so it would be better had we
> not broken it.
> 
> I think it should in general be fixable by just having those
> pci controllers create an empty memory region to pass in,
> like versatile:
> 
>     memory_region_init(&s->pci_io_space, OBJECT(s), "pci_io", 1ULL << 32);
>     memory_region_init(&s->pci_mem_space, OBJECT(s), "pci_mem", 1ULL << 32);
> 
>     pci_bus_new_inplace(&s->pci_bus, sizeof(s->pci_bus), DEVICE(obj), "pci",
>                         &s->pci_mem_space, &s->pci_io_space,
>                         PCI_DEVFN(11, 0), TYPE_PCI_BUS);
> 
> That doesn't affect where PCI DMA goes. It might also
> require mapping an alias into that region at wherever
> the pci hole is on those boards.
> 
> Kind of awkward to do and test at this point in the release cycle though.
> 
> > 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...
> 
> It gives you a place set the appropriate PCI controller or device
> register status bits on abort by a PCI device access, IIRC.

Right, thanks for pointing this out. This was indeed the patches direction.

But even the first patch has meaning by itself and not just a preparation.
As I mentioned in other mail in this thread "read all-ones/ignore writes"
is not implemented yet asbeacuse unassigned_mem_ops has no read/write methods
and valid.accepts returns false.

Thanks,
Marcel

> 
> -- PMM
>