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

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Message-ID: <YB3fCO+QOXaR2Kcj@google.com>
Date:   Fri, 5 Feb 2021 16:12:56 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Ben Gardon <bgardon@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Peter Xu <peterx@...hat.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 Wed, Feb 03, 2021, Paolo Bonzini wrote:
> On 03/02/21 18:46, Ben Gardon wrote:
> > enum kvm_mmu_lock_mode lock_mode =
> > get_mmu_lock_mode_for_root(vcpu->kvm, vcpu->arch.mmu->root_hpa);
> > ....
> > kvm_mmu_lock_for_mode(lock_mode);
> > 
> > Not sure if either of those are actually clearer, but the latter
> > trends in the direction the RCF took, having an enum to capture
> > read/write and whether or not yo yield in a lock mode parameter.
> 
> Could be a possibility.  Also:
> 
> enum kvm_mmu_lock_mode lock_mode =
>   kvm_mmu_lock_for_root(vcpu->kvm, vcpu->arch.mmu->root_hpa);
> 
> kvm_mmu_unlock(vcpu->kvm, lock_mode);
> 
> Anyway it can be done on top.

Maybe go with a literal name, unless we expect additional usage?  E.g. 
kvm_mmu_(un)lock_for_page_fault() isn't terrible.

I'm not a fan of the kvm_mmu_lock_for_root() variants.  "for_root" doesn't have
an obvious connection to the page fault handler or to the read/shared mode of
the TDP.  But, the name is also specific enough to pique my curiosity and make
me wonder what's it's doing.