linux-kernel - Re: [6.5.0-rc1] unchecked MSR access error: RDMSR from 0xe2 at rIP: 0xffffffff87090227 (native_read_msr+0x7/0x40) (intel_idle_init_cstates

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Date:   Tue, 11 Jul 2023 07:26:26 -0700
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Bruno Goncalves <bgoncalv@...hat.com>
Cc:     rafael.j.wysocki@...el.com, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [6.5.0-rc1] unchecked MSR access error: RDMSR from 0xe2 at rIP:
 0xffffffff87090227 (native_read_msr+0x7/0x40) (intel_idle_init_cstates_icpu)

> 
> Oohh, this vm-guest mode is new :/ But it doesn't make sense, that
> commit babbles something about waking CPUs from idle to do TLB
> invalidate, but that shouldn't be the case, that's what we have
> kvm_flush_tlb_multi() for, it should avoid the IPI and flush on
> vcpu-enter.
> 
> Arjan, what is the actual problem you're trying to solve any why hide
> this in intel_idle ?

I'm trying to solve to get guests on par with bare metal in terms of all
the idle capabilities -- including TLB flushing before going idle, but
also all the other latency control mechanisms that cpuidle brings.

And yes this is in intel_idle for 2 reasons
1) we use the host latencies for the deeper C state and that needs intel idle information
2) we are about to add umwait support to this as well (patches on the mailing list for
the base infrastructure for this)


the later is arguable not for 6.5 but is hopefully for 6.6