[MODERATED] Re: [PATCH v8 3/5] NX 3

On Fri, Nov 01, 2019 at 08:07:27AM +0100, speck for Paolo Bonzini wrote:
> On 01/11/19 01:24, speck for Pawan Gupta wrote:
> > On Fri, Nov 01, 2019 at 12:33:45AM +0100, speck for Paolo Bonzini wrote:
> >> From: Paolo Bonzini <[email protected]>
> >> Subject: [PATCH v8 3/5] kvm: mmu: ITLB_MULTIHIT mitigation
> >>  
> >> +	kvm.nx_huge_pages=
> >> +			[KVM] Controls the sw workaround for bug
> >> +			X86_BUG_ITLB_MULTIHIT.
> >> +			force	: Always deploy workaround.
> >> +			off	: Default. Never deploy workaround.
> > 
> > off is not the default in the code, so the default should be "auto" here.
> > 
> >> +			auto	: Deploy workaround based on presence of
> >> +				  X86_BUG_ITLB_MULTIHIT.
> > 
> > Also mitigations=off is not disabling this mitigation. Below patch does
> > that when mitigations=off and kvm.nx_huge_pages=auto.
> > 
> > ---
> > From: Pawan Gupta <[email protected]>
> > Date: Wed, 30 Oct 2019 21:28:24 -0700
> > Subject: [PATCH] kvm: x86: mmu: Apply global mitigations knob to ITLB_MULTIHIT
> > 
> > Problem: The global mitigation knob mitigations=off does not turn off
> > X86_BUG_ITLB_MULTIHIT mitigation.
> > 
> > Fix: Turn off the mitigation when ITLB_MULTIHIT mitigation mode is
> > "auto" and mitigations are turned off globally via cmdline
> > mitigations=off.
> > 
> > Signed-off-by: Pawan Gupta <[email protected]>
> 
> Thanks, I'll post v9 soon.  Are you going to post backports as bundles
> on top of Thomas's?
> 
> Paolo
We (I) have attempted the backports of this and quicly hit issues with the page
zapping changes do to code flux in the upstream.  My troubles started with with
5.2 and 4.19.  I have reached out to an internal resource who is more
knowledgable with KVM mm files to assist with that aspect of the backport.  The
engineer was at a confrence this week and we hope to make more progress next
week once he is back.

--mark