linux-kernel - Re: [PATCH v2 8/8] KVM: x86: Fold decache_cr3() into cache

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Date:   Mon, 30 Sep 2019 08:33:58 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Reto Buerki <reet@...elabs.ch>,
        Liran Alon <liran.alon@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v2 8/8] KVM: x86: Fold decache_cr3() into cache_reg()

On Mon, Sep 30, 2019 at 05:27:58PM +0200, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@...el.com> writes:
> 
> > On Mon, Sep 30, 2019 at 12:58:53PM +0200, Vitaly Kuznetsov wrote:
> >> Sean Christopherson <sean.j.christopherson@...el.com> writes:
> >> 
> >> > Handle caching CR3 (from VMX's VMCS) into struct kvm_vcpu via the common
> >> > cache_reg() callback and drop the dedicated decache_cr3().  The name
> >> > decache_cr3() is somewhat confusing as the caching behavior of CR3
> >> > follows that of GPRs, RFLAGS and PDPTRs, (handled via cache_reg()), and
> >> > has nothing in common with the caching behavior of CR0/CR4 (whose
> >> > decache_cr{0,4}_guest_bits() likely provided the 'decache' verbiage).
> >> >
> >> > Note, this effectively adds a BUG() if KVM attempts to cache CR3 on SVM.
> >> > Opportunistically add a WARN_ON_ONCE() in VMX to provide an equivalent
> >> > check.
> >> 
> >> Just to justify my idea of replacing such occasions with
> >> KVM_INTERNAL_ERROR by setting a special 'kill ASAP' bit somewhere:
> >> 
> >> This WARN_ON_ONCE() falls in the same category (IMO).
> >
> > Maybe something like KVM_BUG_ON?  E.g.:
> >
> > #define KVM_BUG_ON(kvm, cond)		\
> > ({					\
> > 	int r;				\
> > 					\
> > 	if (r = WARN_ON_ONCE(cond))	\
> > 		kvm->vm_bugged = true;	\
> > 	r;				\
> > )}
> > 	
> 
> Yes, that's more or less what I meant! (to me 'vm_bugged' sounds like
> there was a bug in the VM but the bug is actually in KVM so maybe
> something like 'kvm_internal_bug' to make it explicit?)

Ya, kvm_internal_bug is better.