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Re: Howto read MSR thermal under XEN-4.15.0
- To: Julien Grall <julien@xxxxxxx>, Bobbi Sanchez <bobbisanchez@xxxxxx>, <Xen-users@xxxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 17 Jun 2021 12:17:19 +0100
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- List-id: Xen user discussion <xen-users.lists.xenproject.org>
On 17/06/2021 12:09, Julien Grall wrote:
> (+ Andrew and Jan)
>
> Hi,
>
> On 16/06/2021 23:39, Bobbi Sanchez wrote:
>> Hi,
>>
>> 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.
This method was never safe to begin with, because dom0 is just a VM and
can be migrated around. If you pin dom0, then you're still can't access
registers who's scope is missing from where dom0 is pinned.
I'm afraid this is something which has never worked correctly under Xen,
but used to give enough of an illusion of working for people to think
that it did work.
Someone needs to come up with a plan to paravirtualise this interface,
probably using XENPLAT_resource_op, so tools in dom0 can actually read
the registers they think they're trying to access.
~Andrew
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