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Re: [PATCH v2 1/4] xl: Add support for ignore_msrs option

On 18.02.2021 16:52, Roger Pau Monné wrote:
> On Thu, Feb 18, 2021 at 12:54:13PM +0100, Jan Beulich wrote:
>> On 18.02.2021 11:42, Roger Pau Monné wrote:
>>> Not that you need to implement the full thing now, but maybe we could
>>> have something like:
>>> "
>>> =item B<ignore_msrs=[ "MSR_RANGE, "MSR_RANGE", ..]>
>>> Specify a list of MSR ranges that will be ignored by the hypervisor:
>>> reads will return zeros and writes will be discarded without raising a
>>> #GP.
>>> Each MSR_RANGE is given in hexadecimal format and may be a range, e.g.
>>> c00102f0-c00102f1 (inclusive), or a single MSR, e.g. c00102f1.
>>> "
>>> Then you can print the messages in the hypervisor using a guest log
>>> level and modify it on demand in order to get more verbose output?
>> "Modify on demand"? Irrespective of what you mean with this, ...
>>> I don't think selecting whether the messages are printed or not from
>>> xl is that helpful as the same could be achieved using guest_loglvl.
>> ... controlling this via guest_loglvl would affect various other
>> log messages' visibility.
> Right, but do we really need this level of per-guest log control,
> implemented in this way exclusively for MSRs?
> We don't have a way for other parts of the code to have such
> fine-grained control about what messages should be printed, and I
> don't think MSR should be an exception. I assume this would be used to
> detect which MSRs a guest is trying to access, and I would be fine
> just using guest_loglvl to that end, the more that it can be modified
> at run time now.

I can certainly see your point. The problem is that for guests
heavily accessing such MSRs, all other messages may disappear
due to rate limiting. That's not going to be helpful.




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