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

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Message-ID: <edfadb98-b86e-6d03-bdfc-9025fac73dee@redhat.com>
Date:   Tue, 4 May 2021 22:26:18 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Cc:     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 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.

Paolo