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

[Paolo Bonzini <pbonzini@redhat.com>]

Il 08/11/2013 11:44, Peter Maydell ha scritto:
> On 8 November 2013 08:05, Paolo Bonzini <pbonzini@redhat.com> 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.

Yes, for now we should just revert the patch.

BTW I tried optimizing MMIO dispatch and managed to save ~30 cycles so I
don't think we should be afraid of increasing the depth of the radix
tree.  All stuff for 1.8 though.

Paolo

Paolo