[Xen-devel] string mmio/pio across page boundaries

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

When preparing arguments for send_mmio_req() or send_pio_req() in hvm
where a single iteration crosses a page boundary, the value to be written
is copied from guest memory, but I can't see where the value read is copied
to guest memory. Is this case simply missing?

Also, a long while back the logic to calculate when wrapping occurs was
changed with two subsequent patches. As I'm looking at the code now it
seems like
- only the first patch got applied to handle_mmio() (i.e., the logic is still
  broken
- neither patch got applied to {svm,vmx}_io_instruction().

Further, there is a comment in handle_mmio() now saying "We need to
make sure we advance to the point where the next request will be on a
different page.  If we're going down, that means advancing until one
byte before the start of the page, hence +1." This wasn't applied
similarly to {svm,vmx}_io_instruction(). And the actual code seems
wrong: If e.g. addr is on a page boundary, count will become zero. I
would think that the +1 must be outside of the division.

Was this intentional in some way? Otherwise, I'll prepare a patch to
address all of these.

Thanks, Jan

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