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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Message-ID: <20230711132553.GN3062772@hirez.programming.kicks-ass.net>
Date:   Tue, 11 Jul 2023 15:25:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bruno Goncalves <bgoncalv@...hat.com>
Cc:     arjan@...ux.intel.com, 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)

On Tue, Jul 11, 2023 at 02:55:57PM +0200, Peter Zijlstra wrote:

> 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 ?


static __always_inline int __intel_idle_hlt(struct cpuidle_device *dev,
					struct cpuidle_driver *drv, int index)
{
	raw_safe_halt();
	raw_local_irq_disable();
	return index;
}

Which does:

	STI
	HLT
	CLI

static __cpuidle int intel_idle_hlt_irq_on(struct cpuidle_device *dev,
                                   struct cpuidle_driver *drv, int index)
{
       int ret;

       raw_local_irq_enable();
       ret = __intel_idle_hlt(dev, drv, index);
       raw_local_irq_disable();

       return ret;
}

That is nonsensical code; because now you have:

	STI
	STI
	HLT
	CLI
	CLI

And that makes sense how?

Rafael, can we please just pull these patches and try again later?