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Date:   Tue, 11 Jul 2023 15:15:57 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Bruno Goncalves <bgoncalv@redhat.com>
Cc:     arjan@linux.intel.com, rafael.j.wysocki@intel.com, x86@kernel.org,
        LKML <linux-kernel@vger.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)
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On Tue, Jul 11, 2023 at 02:55:57PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 11, 2023 at 02:25:51PM +0200, Bruno Goncalves wrote:
> 
> > R640 2x  Intel(R) Xeon(R) Silver 4116 CPU @ 2.10GHz
> 
> Gawd, I hate our naming :/ Google tells me that is a skylake.
> 
> > and start the VM with:
> > 
> > -accel kvm -cpu
> > Skylake-Server-IBRS,ss=on,vmx=on,pdcm=on,hypervisor=on,tsc-adjust=on,clflushopt=on,umip=on,pku=on,md-clear=on,stibp=on,arch-capabilities=on,ssbd=on,xsaves=on,ibpb=on,ibrs=on,amd-stibp=on,amd-ssbd=on,rsba=on,skip-l1dfl-vmentry=on,pschange-mc-no=on
> 
> You tell it to be a skylake
> 
> > The decoded call trace:
> 
> > /builds/4626306068/workdir/drivers/idle/intel_idle.c:1820
> 
> And that's skx_idle_state_table_update() reading
> MSR_PKG_CST_CONFIG_CONTROL and that code has been around since 2021.
> 
> So things are somewhat consistent. But I find it weird that intel_idle
> gets selected for a guest, I'm not exactly sure what's up with that.
> 
> 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 ?

Also, I thought we already had a virt specific cpuidle driver
somewhere....

/me rummages around and finds cpuidle-haltpoll.c. That thing was
specifically created for virt IIRC. Can we please stick all the virt
stuff in there? That seems far simpler to extend anyway.

Rafael?