linux-kernel - Re: [PATCH 4.19 009/191] KVM: nVMX: Use correct root level for nested EPT shadow page tables

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Date:   Sat, 22 Feb 2020 08:40:47 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Pavel Machek <pavel@...x.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 009/191] KVM: nVMX: Use correct root level for
 nested EPT shadow page tables

Hi!

> > > Hardcode the EPT page-walk level for L2 to be 4 levels, as KVM's MMU
> > > currently also hardcodes the page walk level for nested EPT to be 4
> > > levels.  The L2 guest is all but guaranteed to soft hang on its first
> > > instruction when L1 is using EPT, as KVM will construct 4-level page
> > > tables and then tell hardware to use 5-level page tables.
> > 
> > I don't get it. 7/191 reverts the patch, then 9/191 reverts the
> > revert. Can we simply drop both 7 and 9, for exactly the same result?
> >
> > (Patch 8 is a unused file, so it does not change the picture).
> 
> Patch 07 is reverting this patch from the same unused file, 
> arch/x86/kvm/vmx/vmx.c[*].  The reason patch 07 looks like a normal diff is
> that a prior patch in 4.19.105 created the unused file (which is what's
> reverted by patch 08 here).
> 
> Patch 09 reintroduces the fix for the correct file, arch/x86/kvm/vmx.c.

Aha, thanks, I checked content few times but missed difference in
filename. Now it makes sense.

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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