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Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensi
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive |
Date: |
Thu, 23 Feb 2017 16:47:23 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
On 23/02/2017 16:39, Alex Williamson wrote:
> On Thu, 23 Feb 2017 16:21:47 +0100
> Paolo Bonzini <address@hidden> wrote:
>
>> On 23/02/2017 15:35, Peter Maydell wrote:
>>> On 23 February 2017 at 12:53, Paolo Bonzini <address@hidden> wrote:
>>>>
>>>>
>>>> On 23/02/2017 13:26, Peter Maydell wrote:
>>>>> On 23 February 2017 at 11:43, Paolo Bonzini <address@hidden> wrote:
>>>>>> On 23/02/2017 12:34, Peter Maydell wrote:
>>>>>>> We should probably update the doc comment to note that the
>>>>>>> pointer is to host-endianness memory (and that this is not
>>>>>>> like normal RAM which is target-endian)...
>>>>>>
>>>>>> I wouldn't call it host-endianness memory, and I disagree that normal
>>>>>> RAM is target-endian---in both cases it's just a bunch of bytes.
>>>>>>
>>>>>> However, the access done by the MemoryRegionOps callbacks needs to match
>>>>>> the endianness declared by the MemoryRegionOps themselves.
>>>>>
>>>>> Well, if the guest stores a bunch of integers to the memory, which
>>>>> way round do you see them when you look at the bunch of bytes?
>>>>
>>>> You see them in whatever endianness the guest used.
>>>
>>> I'm confused. I said "normal RAM and this ramdevice memory are
>>> different", and you seem to be saying they're the same. I don't
>>> think they are (in particular I think with a BE guest on an
>>> LE host they'll look different).
>>
>> No, they look entirely the same. The only difference is that they go
>> through MemoryRegionOps instead of memcpy.
>
> Is this true for vfio use case? If we use memcpy we're talking directly
> to the device with no endian conversions. If we use read/write then
> there is an endian conversion in the host kernel.
But ramd MemoryRegionOps do not use file read/write, they use memory
read/write, so they talk directly to the device.
Paolo
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, (continued)
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Peter Maydell, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Paolo Bonzini, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Peter Maydell, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Paolo Bonzini, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Peter Maydell, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Paolo Bonzini, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Yongji Xie, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, David Gibson, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Paul Mackerras, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Alex Williamson, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Alex Williamson, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, David Gibson, 2017/02/23
- Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Alexey Kardashevskiy, 2017/02/23
Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive, Michael Roth, 2017/02/26