Re: [Xen-devel] [PATCH v6 09/16] x86/hvm: limit reps to avoid the need to handle retry

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 03/07/15 17:25, Paul Durrant wrote:
> By limiting hvmemul_do_io_addr() to reps falling within the page on which
> a reference has already been taken, we can guarantee that calls to
> hvm_copy_to/from_guest_phys() will not hit the HVMCOPY_gfn_paged_out
> or HVMCOPY_gfn_shared cases. Thus we can remove the retry logic (added
> by c/s 82ed8716b "fix direct PCI port I/O emulation retry and error
> handling") from the intercept code and simplify it significantly.
>
> Normally hvmemul_do_io_addr() will only reference single page at a time.
> It will, however, take an extra page reference for I/O spanning a page
> boundary.
>
> It is still important to know, upon returning from x86_emulate(), whether
> the number of reps was reduced so the mmio_retry flag is retained for that
> purpose.
>
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Cc: Keir Fraser <keir@xxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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