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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 08:28:02 +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.
Yeah, that's what happens when you read mails too early in the morning :). The
xen branch didn't get pulled yet, so upstream is missing the following patch:
commit f221e5ac378feea71d9857ddaa40f829c511742f
Author: Stefano Stabellini <address@hidden>
Date: Mon Jun 27 18:26:06 2011 +0100
qemu_ram_ptr_length: take ram_addr_t as arguments
qemu_ram_ptr_length should take ram_addr_t as argument rather than
target_phys_addr_t because is doing comparisons with RAMBlock addresses.
cpu_physical_memory_map should create a ram_addr_t address to pass to
qemu_ram_ptr_length from PhysPageDesc phys_offset.
Remove code after abort() in qemu_ram_ptr_length.
Changes in v2:
- handle 0 size in qemu_ram_ptr_length;
- rename addr1 to raddr;
- initialize raddr to ULONG_MAX.
Signed-off-by: Stefano Stabellini <address@hidden>
Reviewed-by: Peter Maydell <address@hidden>
Signed-off-by: Alexander Graf <address@hidden>
Anthony?
Alex