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Re: [XEN PATCH] intel/msr: Fix handling of MSR_RAPL_POWER_UNIT
- To: Teddy Astie <teddy.astie@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 14 Jan 2025 09:41:47 +0000
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Tue, 14 Jan 2025 09:41:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13/01/2025 6:42 pm, Teddy Astie wrote:
> Solaris 11.4 tries
Is it only Solaris 11.4, or is the simply the one repro you had?
Have you reported a bug?
> to access this MSR on some Intel platforms without properly
> setting up a proper #GP handler, which leads to a immediate crash.
Minor grammar note. Either "without a proper #GP handler" or "without
properly setting up a #GP handler", but having two proper(ly)'s in there
is less than ideal.
> Emulate the access of this MSR by giving it a legal value (all values set to
> default, as defined by Intel SDM "RAPL Interfaces").
>
> Fixes: 84e848fd7a1 ('x86/hvm: disallow access to unknown MSRs')
> Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
> ---
> Does it have a risk of negatively affecting other operating systems expecting
> this MSR read to fail?
It's Complicated.
RAPL is a non-architectural feature (on Intel; AMD did it properly). It
does not have a CPUID bit to announce the presence of the MSRs.
Therefore OSes use a mixture of model numbers and {wr,rd}msr_safe() to
probe.
I expect this will change the behaviour of Linux.
~Andrew
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