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Re: [Qemu-devel] [PATCH v2 4/5] exec.c: refactor cpu_physical_memory_map
From: |
Alexander Graf |
Subject: |
Re: [Qemu-devel] [PATCH v2 4/5] exec.c: refactor cpu_physical_memory_map |
Date: |
Tue, 12 Jul 2011 08:21:36 +0200 |
On 12.07.2011, at 00:17, Jan Kiszka wrote:
> On 2011-05-19 19:35, address@hidden wrote:
>> From: Stefano Stabellini <address@hidden>
>>
>> Introduce qemu_ram_ptr_length that takes an address and a size as
>> parameters rather than just an address.
>>
>> Refactor cpu_physical_memory_map so that we call qemu_ram_ptr_length only
>> once rather than calling qemu_get_ram_ptr one time per page.
>> This is not only more efficient but also tries to simplify the logic of
>> the function.
>> Currently we are relying on the fact that all the pages are mapped
>> contiguously in qemu's address space: we have a check to make sure that
>> the virtual address returned by qemu_get_ram_ptr from the second call on
>> is consecutive. Now we are making this more explicit replacing all the
>> calls to qemu_get_ram_ptr with a single call to qemu_ram_ptr_length
>> passing a size argument.
>
> This breaks cpu_physical_memory_map for >4G addresses on PC.
> Effectively, it doesn't account for the PCI gap, ie. that the RAM block
> is actually mapped in two chunks into the guest physical memory. One
> outcome is that QEMU aborts when we try to process an address that is
> now "outside" RAM. Simple to reproduce with a virtio NIC and 5G guest
> memory, even without KVM.
Ah, I see what you mean now. It breaks on current HEAD, but not on my last
xen-next branch which already included that patch, so I'd assume it's something
different that came in later.
Alex