Re: [Xen-devel] [PATCH] xen: Filter out MSR write events

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/04/16 05:26, Razvan Cojocaru wrote:
> On 04/11/16 22:18, Konrad Rzeszutek Wilk wrote:
>> On Mon, Apr 11, 2016 at 07:41:54PM +0300, Razvan Cojocaru wrote:
>>> This patch only allows introspection-related MSR write events to
>>> be sent out, improving performance. Should additional events be
>>> required, they can then simply be added to the list of
>>> vmx_introspection_force_enabled_msrs[].
>>>
>>> Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>>
>> Thought should there be some .. dynamic mechanism to update
>> the MSR list? Or remove entries (or temporarily blacklist
>> the built-one ins), etc?
> While this should be enough for now (the introspection MSR list is very
> small, and we're probably the only consumers), that's indeed the way for
> the future, I think. We should have a set-like container of unique
> elements that can grow and shrink and can be searched quickly, and add /
> remove MSRs we're interested in there.
>
> The CR write events bitmap approach clearly doesn't work, as there are
> too many MSRs to be able to select them all with a bitmap in the future.

The current intercept bitmaps have 4x1K bitmaps, a read and a write bit
for the low and high MSR indices.

For introspection purposes, you will also want a bitmap covering the
hypervisor range.  For now, 3x1K bitmaps should be plenty to cover all
potentially interesting MSRs.

~Andrew

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