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

[Dylanger Daly <dylanger@thegrail.co>]

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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@citrix.com>
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@thegrail.co>
>
> 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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