Re: An issue with x86 tcg and MMIO

[Peter Maydell]

On Thu, 2 Feb 2023 at 12:31, Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Thu, 2 Feb 2023 11:39:28 +0000
> Peter Maydell <peter.maydell@linaro.org> wrote:
> > You might want to look at whether QEMU's iommu functionality is helpful
> > to you -- I'm assuming CXL doesn't do weird stuff on a less-than-page
> > granularity, and the iommu APIs will let you do "programmatically decide
> > where this address should actually go". The other option involves
> > mapping and unmapping MemoryRegions inside a container MR.
>
> Unfortunately it does weird stuff well below a page granularity.
> Interleaving is down to 256 bytes.

That's unfortunate...

At any rate, conceptually we ought to be able to execute from
an instruction that overlaps between actual-RAM and an MMIO
MemoryRegion; it would be nice if we could fall back to the
execute-and-discard approach for that in the same way as if
the entire insn was in MMIO.

-- PMM