linux-kernel - Re: [PATCH 05/14] KVM: x86/mmu: Consult max mapping level when zapping collapsible SPTEs

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Message-ID: <YC6UmukeFlrdWAxe@google.com>
Date:   Thu, 18 Feb 2021 08:23:54 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Makarand Sonare <makarandsonare@...gle.com>
Subject: Re: [PATCH 05/14] KVM: x86/mmu: Consult max mapping level when
 zapping collapsible SPTEs

On Thu, Feb 18, 2021, Paolo Bonzini wrote:
> On 13/02/21 01:50, Sean Christopherson wrote:
> > 
> >  		pfn = spte_to_pfn(iter.old_spte);
> >  		if (kvm_is_reserved_pfn(pfn) ||
> > -		    (!PageTransCompoundMap(pfn_to_page(pfn)) &&
> > -		     !kvm_is_zone_device_pfn(pfn)))
> > +		    iter.level >= kvm_mmu_max_mapping_level(kvm, slot, iter.gfn,
> > +							    pfn, PG_LEVEL_NUM))
> >  			continue;
> 
> 
> This changes the test to PageCompound.  Is it worth moving the change to
> patch 1?

Yes?  I originally did that in a separate patch, then changed my mind.

If PageTransCompoundMap() also detects HugeTLB pages, then it is the "better"
option as it checks that the page is actually mapped huge.  I dropped the change
because PageTransCompound() is just a wrapper around PageCompound(), and so I
assumed PageTransCompoundMap() would detect HugeTLB pages, too.  I'm not so sure
about that after rereading the code, yet again.