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Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensi
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive |
Date: |
Thu, 23 Feb 2017 08:39:08 -0700 |
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.
- 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, 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, 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 <=
- 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, 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