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Re: [Qemu-devel] [PATCH 2/3] memory: add API for creating ROM/device reg
From: |
Alexander Graf |
Subject: |
Re: [Qemu-devel] [PATCH 2/3] memory: add API for creating ROM/device regions |
Date: |
Sun, 14 Aug 2011 08:43:37 -0700 |
Am 14.08.2011 um 06:29 schrieb Anthony Liguori <address@hidden>:
> On 08/13/2011 10:05 PM, Avi Kivity wrote:
>> On 08/12/2011 06:48 AM, Anthony Liguori wrote:
>>>> target_phys_addr_t offset_in_region;
>>>> AddrRange addr;
>>>> uint8_t dirty_log_mask;
>>>> + bool readable;
>>> @@ -125,6 +125,7 @@ struct FlatRange {
>>>
>>> In a follow up, it might be good to add a comment explaining that this
>>> whole readable thing is not just an optimization, but a hard
>>> requirement for KVM in order to be able to execute code from ROM.
>>
>> This has nothing to do with kvm (in fact, I think we cannot support it
>> under kvm with current interfaces). It's there to support devices that
>> sometimes act as RAM and sometimes as mmio.
>
> That is not a functional behavior but rather an optimization. Functionally
> speaking, there is absolutely no different between "acting as RAM" and
> "acting as mmio".
>
> But you cannot remove the optimization because of the aforementioned
> limitation in KVM.
>
> Maybe it's just me but I find this to be a very subtle detail so a comment
> would be helpful :-)
Well, TCG also can't execute from MMIO, right? So it's at least not KVM
specific - TCG also gets the speedup from mapping roms as ram.
Alex
>
[Qemu-devel] [PATCH 1/3] memory: reclaim resources when a memory region is destroyed for good, Avi Kivity, 2011/08/08
[Qemu-devel] [PATCH 3/3] memory: correct documentation typos, Avi Kivity, 2011/08/08
Re: [Qemu-devel] [PATCH 0/3] Memory API updates, Anthony Liguori, 2011/08/12