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Re: [Xen-devel] [PATCH] hvm: Allow HVM guests to make console_io hypercall.

On 09/30/2013 04:04 AM, Jan Beulich wrote:
On 27.09.13 at 23:17, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
The console_io hypercall is provided for PV guests and for HVM
guests it is done via the 0xe9 port. However the PV hypercall
is more efficient as it takes a string rather than one character
per write.

While the change itself is fine, there are two questions arising
from me looking at do_console_io() in this context:

1) While I can see why VERBOSE ought to control access to
CONSOLEIO_write, I would think CONSOLEIO_read ought to be
constrained to the control domain in any case.

I agree on read. Do we still need the restriction on write with
non-VERBOSE builds now that domains' output is restricted to the
guest debug loglevel? I recall this being discussed briefly when
the output changes were being made, but I believe the decision
was only that such a change belonged in a different patch.

2) xsm_console_io(), like quite a few other stubs in xsm/dummy.h,
ignores its "d" parameter and uses current->domain instead. Is
that really the right way (and if so, why are there other stubs
that do honor their inputs)?


No, this is incorrect - it should be using the parameter, same as
any of the other stubs that have a parameter that is always set
to current->domain.

Daniel De Graaf
National Security Agency

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