Re: [Xen-devel] [PATCH] Add Undervolt MSRs to wrmsr function.

[Dylanger Daly <dylanger@xxxxxxxxxxx>]

No worries Andrew, it was my first patch, thank you for the response.

It's based on Xen 4.8

Dom0 should be controlling it, but I wasn't aware of the Security implications.

The scope isn't well documented:

 https://ressman.org/posts/2018-06-26-voltage-temperature-tdp-thinkpad/

More experimental as it worked with my Laptop.

Thank you for your time

On Thu, Apr 18, 2019, 10:09 AM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:

On 18/04/2019 09:56, Dylanger Daly wrote:
> Giving Laptop Users the ability to Undervolt and change Temp Throttle Limits.
>
> Signed-off-by: Dylanger Daly <dylanger@xxxxxxxxxxx>

Thankyou for the patch.  Which version of Xen is it against?  It is
fairly old, given that the function you patch has now moved to
arch/x86/pv/emul-priv-op.c.  Furthermore, this is the legacy path, so
the functions this should be added to are guest_{rdmsr,wrmsr}() in
arch/x86/msr.c

What entity is controlling this?

Sadly, there are a number of issues.  You open these MSRs up to
unprivileged domUs, and there is a mismatch between the vcpus/pcpus.

What is the scope of these MSRs?  I guess dom0 is going to write them on
all cores, but as dom0 gets scheduled around, this wont match up with
the pcpus across the host.

~Andrew

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