Re: [Xen-devel] [PATCH 1/2] x86/HVM: suppress I/O completion for port output

[Juergen Gross <jgross@xxxxxxxx>]

On 09/04/18 15:23, Jan Beulich wrote:
> We don't break up port requests in case they cross emulation entity
> boundaries, and a write to an I/O port is necessarily the last
> operation of an instruction instance, so there's no need to re-invoke
> the full emulation path upon receiving the result from an external
> emulator.
> 
> In case we want to properly split port accesses in the future, this
> change will need to be reverted, as it would prevent things working
> correctly when e.g. the first part needs to go to an external emulator,
> while the second part is to be handled internally.
> 
> While this addresses the reported problem of Windows paging out the
> buffer underneath an in-process REP OUTS, it does not address the wider
> problem of the re-issued insn (to the insn emulator) being prone to
> raise an exception (#PF) during a replayed, previously successful memory
> access (we only record prior MMIO accesses).
> 
> Leaving aside the problem tried to be worked around here, I think the
> performance aspect alone is a good reason to change the behavior.
> 
> Also take the opportunity and change bool_t -> bool as
> hvm_vcpu_io_need_completion()'s return type.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Release-acked-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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