Re: [PATCH] xen: Filter out MSR write events

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 12/04/16 11:17, Razvan Cojocaru wrote:
> On 04/12/2016 12:38 PM, Andrew Cooper wrote:
>> 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@bitdefender.com>
>>>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>>>
>>>> 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.
> I see, so for future reference, add a pointer member allocated with
> alloc_xenheap_page() and memset() to 0 to struct arch_domain, maybe
> named monitor_msrs_bitmap (while removing mov_to_msr_enabled and
> mov_to_msr_extended from struct monitor)? This could get allocated on
> vm_event_init_domain() and de-allocated on vm_event_cleanup_domain().

Looks suitable.

~Andrew

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