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Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size functio
From: |
Ethan Chen |
Subject: |
Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented |
Date: |
Mon, 30 Oct 2023 14:00:54 +0800 |
User-agent: |
Mutt/2.1.4 (2021-12-11) |
On Fri, Oct 27, 2023 at 12:13:50PM -0400, Peter Xu wrote:
> Add cc list.
>
> On Fri, Oct 27, 2023 at 12:02:24PM -0400, Peter Xu wrote:
> > On Fri, Oct 27, 2023 at 11:28:36AM +0800, Ethan Chen wrote:
> > > On Thu, Oct 26, 2023 at 10:20:41AM -0400, Peter Xu wrote:
> > > > Could you elaborate why is that important? In what use case?
> > > I was not involved in the formulation of the IOPMP specification, but
> > > I'll try
> > > to explain my perspective. IOPMP use the same the idea as PMP. "The
> > > matching
> > > PMP entry must match all bytes of an access, or the access fails."
> > >
> > > >
> > > > Consider IOVA mapped for address range iova=[0, 4K] only, here we have a
> > > > DMA request with range=[0, 8K]. Now my understanding is what you want
> > > > to
> > > > achieve is don't trigger the DMA to [0, 4K] and fail the whole [0, 8K]
> > > > request.
> > > >
> > > > Can we just fail at the latter DMA [4K, 8K] when it happens? After all,
> > > > IIUC a device can split the 0-8K DMA into two smaller DMAs, then the 1st
> > > > chunk can succeed then if it falls in 0-4K. Some further explanation of
> > > > the failure use case could be helpful.
> > >
> > > IOPMP can only detect partially hit in an access. DMA device will split a
> > > large DMA transfer to small DMA transfers base on target and DMA transfer
> > > width, so partially hit error only happens when an access cross the
> > > boundary.
> > > But to ensure that an access is only within one entry is still important.
> > > For example, an entry may mean permission of a device memory region. We
> > > do
> > > not want to see one DMA transfer can access mutilple devices, although
> > > DMA
> > > have permissions from multiple entries.
> >
> > I was expecting a DMA request can be fulfilled successfully as long as the
> > DMA translations are valid for the whole range of the request, even if the
> > requested range may include two separate translated targets or more, each
> > point to different places (either RAM, or other devicie's MMIO regions).
IOPMP is used to check DMA translation is vaild or not. In IOPMP specification
, a translation access more than one entry is not invalid.
Though it is not recommand, user can create an IOPMP entry contains mutiple
places to make this kind translations valid.
> >
> > AFAIK currently QEMU memory model will automatically split that large
> > request into two or more smaller requests, and fulfill them separately by
> > two/more IOMMU translations, with its memory access dispatched to the
> > specific memory regions.
Because of requests may be split, I need a method to take the original request
information to IOPMP.
> >
> > The example you provided doesn't seem to be RISCV specific. Do you mean it
> > is a generic requirement from PCI/PCIe POV, or is it only a restriction of
> > IOPMP? If it's a valid PCI restriction, does it mean that all the rest
> > IOMMU implementations in QEMU currently are broken?
> >
It only a restriction of IOPMP.
Thanks,
Ethan Chen
- Re: [PATCH 1/6] exec/memory: Introduce the translate_size function within the IOMMU class, (continued)
[PATCH 4/6] Add RISC-V IOPMP support, Ethan Chen, 2023/10/25
[PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented, Ethan Chen, 2023/10/25
- Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented, Peter Xu, 2023/10/25
- Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented, Ethan Chen, 2023/10/26
- Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented, Peter Xu, 2023/10/27
- Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented, Peter Xu, 2023/10/27
- Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented,
Ethan Chen <=
- Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented, Peter Xu, 2023/10/30
- Re: [PATCH 2/6] system/physmem: IOMMU: Invoke the translate_size function if it is implemented, Ethan Chen, 2023/10/31
[PATCH 3/6] exec/memattrs: Add iopmp source id to MemTxAttrs, Ethan Chen, 2023/10/25
[PATCH 5/6] hw/dma: Add Andes ATCDMAC300 support, Ethan Chen, 2023/10/25
[PATCH 6/6] hw/riscv/virt: Add IOPMP support, Ethan Chen, 2023/10/25
Re: [PATCH 0/6] Support RISC-V IOPMP, Ethan Chen, 2023/10/26