linux-kernel - Re: [PATCH v2 23/28] KVM: x86/mmu: Allow parallel page faults for the TDP MMU

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Message-ID: <d2c4ae90-1e60-23ed-4bda-24cf88db04c9@redhat.com>
Date:   Wed, 3 Feb 2021 13:39:53 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...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 23/28] KVM: x86/mmu: Allow parallel page faults for the
 TDP MMU

On 02/02/21 19:57, Ben Gardon wrote:
> 
> -	write_lock(&vcpu->kvm->mmu_lock);
> +
> +	if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> +		read_lock(&vcpu->kvm->mmu_lock);
> +	else
> +		write_lock(&vcpu->kvm->mmu_lock);
> +

I'd like to make this into two helper functions, but I'm not sure about 
the naming:

- kvm_mmu_read_lock_for_root/kvm_mmu_read_unlock_for_root: not precise 
because it's really write-locked for shadow MMU roots

- kvm_mmu_lock_for_root/kvm_mmu_unlock_for_root: not clear that TDP MMU 
operations will need to operate in shared-lock mode

I prefer the first because at least it's the conservative option, but 
I'm open to other opinions and suggestions.

Paolo