linux-kernel - Re: KVM broken after suspend in most recent kernels.

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Date:   Wed, 27 May 2020 15:28:50 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Brad Campbell <lists2009@...rfbargle.com>
Cc:     kvm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: KVM broken after suspend in most recent kernels.

On Tue, 2020-05-26 at 22:13 -0700, Sean Christopherson wrote:
> On Mon, May 25, 2020 at 09:15:57PM +0800, Brad Campbell wrote:
> > > When you mean that KVM is broken after suspend, you mean that you
> > > can't
> > > start new VMs after suspend, or do VMs that were running before
> > > suspend
> > > break?  I see the later on my machine. I have AMD system though,
> > > so most
> > > likely this is another bug.
> > > 
> > > Looking at the commit, I suspect that we indeed should set the
> > > IA32_FEAT_CTL
> > > after resume from ram, since suspend to ram might count as a
> > > complete CPU
> > > reset.
> > > 
> > 
> > One of those "I should have clarified that" moments immediately
> > after I
> > pressed send.  I've not tried suspending with a VM running. It's
> > "can't start
> > new VMs after suspend".
> 
> Don't bother testing suspending with a VM, the only thing that will
> be
> different is that your system will hang on resume instead when
> running a
> VM.  If there are active VMs, KVM automatically re-enables VMX via
> VMXON
> after resume, and VMXON is what's faulting.
> 
> Odds are good the firmware simply isn't initializing IA32_FEAT_CTL,
> ever.
> The kernel handles the boot-time case, but I (obviously) didn't
> consider
> the suspend case.  I'll work on a patch.

This is exactly what I was thinking about this as well.

Best regards,
	Maxim Levitsky
>