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Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API
From: |
Ian Jackson |
Subject: |
Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API |
Date: |
Tue, 20 Jan 2009 14:49:00 +0000 |
Avi Kivity writes ("Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping
API"):
> The devices we're talking about here don't have a DMA count register.
Which devices ? All devices ever that want to do zero-copy DMA into
the guest ?
> They are passed scatter-gather lists, and I don't think they make
> guarantees about the order in which they're accessed.
Many devices will be able to make such promises.
> This DMA will be into RAM, not mmio.
As previously discussed, we might be using bounce buffers even for
RAM, depending on the execution model. You said earlier:
Try it out. I'm sure it will work just fine (if incredibly slowly,
unless you provide multiple bounce buffers).
but here is an example from Jamie of a situation where it won't work
right.
> We don't have a reliable amount to pass.
A device which _really_ doesn't have a reliable amount to pass, and
which is entitled to scribble all over the RAM it was to DMA to even
if it does only a partial transfer, can simply pass the total transfer
length. That would be no different to your proposal.
Ian.
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, (continued)
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/20
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Ian Jackson, 2009/01/20
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Ian Jackson, 2009/01/19
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/19
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Ian Jackson, 2009/01/19
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/19
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Ian Jackson, 2009/01/20
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/20
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Jamie Lokier, 2009/01/19
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/19
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API,
Ian Jackson <=
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/20
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Jamie Lokier, 2009/01/20
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/20
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Ian Jackson, 2009/01/21
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Ian Jackson, 2009/01/21
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Avi Kivity, 2009/01/21
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Anthony Liguori, 2009/01/21
- Re: [Qemu-devel] [PATCH 1/5] Add target memory mapping API, Ian Jackson, 2009/01/20
- [Qemu-devel] Re: Add target memory mapping API, Mike Day, 2009/01/21
- Re: [Qemu-devel] Re: Add target memory mapping API, Avi Kivity, 2009/01/21