linux-kernel - Re: [PATCH] KVM: x86/mmu: fix potential races when walking host page table

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Date:   Fri, 29 Apr 2022 14:35:43 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Mingwei Zhang <mizhang@...gle.com>,
        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
Subject: Re: [PATCH] KVM: x86/mmu: fix potential races when walking host page
 table

On Fri, Apr 29, 2022, Paolo Bonzini wrote:
> > +out:
> > +	local_irq_restore(flags);
> > +	return level;
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_lookup_address_level_in_mm);
> 
> Exporting is not needed.
> 
> Thanks for writing the walk code though.  I'll adapt it and integrate the
> patch.

But why are we fixing this only in KVM?  I liked the idea of stealing perf's
implementation because it was a seemlingly perfect fit and wouldn't introduce
new code (ignoring wrappers, etc...).

We _know_ that at least one subsystem is misusing lookup_address_in_pgd() and
given that its wrappers are exported, I highly doubt KVM is the only offender.
It really feels like we're passing the buck here by burying the fix in KVM.