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Re: Howto read MSR thermal under XEN-4.15.0

Am 17.06.21 um 13:43 schrieb Andrew Cooper:
On 17/06/2021 12:26, Jan Beulich wrote:
On 17.06.2021 13:09, Julien Grall wrote:
On 16/06/2021 23:39, Bobbi Sanchez wrote:
how can i read the MSR Thermal Values under XEN-4.15.0 ?

Usually without having XEN-4.15.0 installed i can read the MSR Thermal
Values like this:

rdmsr -p 0 -d -f22:16 0x19c

this works for my Core2Quod Q6600.

But after having xen-4.15.0 installed and booted, same command shows now: 0
I believe the access was restricted as part of XSA-351 [1]. I am not
sure if there are a safe generic way to access them. I will let Andrew
and Jan commenting.
just as additional context (i.e. on top of Andrew's reply): It wasn't
that XSA, but our general switch of policy from blacklisting to
whitelisting MSRs. The XSA was about *_POWER_* and *_PERF_* MSRs.
Well - that XSA was the trigger for finally removing default read access
from all VMs, but yes - this specific issue described here only on Xen
4.15 and later.

You can use boot with dom0=msr-relaxed to regain read access, but will
still be subject to all the reasons I explained before about this not
actually working properly.


Hi Andrew,

thanks for hint, but thermal temps are not shown also after appending  that boot paramter to grub "dom0=msr-relxaed"!

 Is there any  other choice to access the thermal temps under xen-4.15.0 ?

Best Regards



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