Re: [Xen-devel] [PATCH v4 16/17] x86/hvm: always re-emulate I/O from a buffer

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.06.15 at 13:24, <paul.durrant@xxxxxxxxxx> wrote:
> If memory mapped I/O is 'chunked' then the I/O must be re-emulated,
> otherwise only the first chunk will be processed. This patch makes
> sure all I/O from a buffer is re-emulated regardless of whether it
> is a read or a write.

I'm not sure I understand this: Isn't the reason for treating reads
and writes differently due to the fact that MMIO reads may have
side effects, and hence can't be re-issued (whereas writes are
always the last thing an instruction does, and hence can't hold up
retiring of it, and hence don't need retrying)?

Furthermore, doesn't "only the first chunk" get represented correctly
already by informing the caller that only a single iteration of a
repeated instruction was done, such that further repeats will get
carried out anyway (resulting in another, fresh cycle through the
emulator)?

Jan


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