linux-kernel - Re: [PATCH v2 1/7] KVM: x86/mmu: Track if shadow MMU active

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Message-ID: <YJGwOfzTtj4kJIVp@google.com>
Date:   Tue, 4 May 2021 20:36:09 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Peter Xu <peterx@...hat.com>,
        Peter Shier <pshier@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>
Subject: Re: [PATCH v2 1/7] KVM: x86/mmu: Track if shadow MMU active

On Tue, May 04, 2021, Paolo Bonzini wrote:
> On 04/05/21 21:55, Sean Christopherson wrote:
> > But, I think we we can avoid bikeshedding by simply eliminating this flag.  More
> > in later patches.
> 
> Are you thinking of checking slot->arch.rmap[0] directly?  That should work
> indeed.
> 
> > > -	kvm_mmu_init_tdp_mmu(kvm);
> > > +	if (!kvm_mmu_init_tdp_mmu(kvm))
> > > +		activate_shadow_mmu(kvm);
> > Doesn't come into play yet, but I would strongly prefer to open code setting the
> > necessary flag instead of relying on the helper to never fail.
> > 
> 
> You mean
> 
> kvm->arch.shadow_mmu_active = !kvm_mmu_init_tdp_mmu(kvm);
> 
> (which would assign to alloc_memslot_rmaps instead if shadow_mmu_active is
> removed)?  That makes sense.

Ya, that or:

	if (kvm_mmu_init_tdp_mmu(kvm))
		kvm->arch.memslots_have_rmaps = true;

I don't have a preference between the two variants.