linux-kernel - Re: [PATCH v2 24/28] KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock

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Message-ID: <7104de85-0b01-a950-91f9-04fb3d5eb1be@redhat.com>
Date:   Wed, 3 Feb 2021 19:32:21 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        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 24/28] KVM: x86/mmu: Allow zap gfn range to operate
 under the mmu read lock

On 03/02/21 19:31, Ben Gardon wrote:
> On Wed, Feb 3, 2021 at 3:26 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>>
>> On 02/02/21 19:57, Ben Gardon wrote:
>>> +#ifdef CONFIG_LOCKDEP
>>> +     if (shared)
>>> +             lockdep_assert_held_read(&kvm->mmu_lock);
>>> +     else
>>> +             lockdep_assert_held_write(&kvm->mmu_lock);
>>> +#endif /* CONFIG_LOCKDEP */
>>
>> Also, there's no need for the #ifdef here.
> 
> I agree, I must have misinterpreted some feedback on a previous commit
> and gone overboard with it.
> 
> 
>> Do we want a helper
>> kvm_lockdep_assert_mmu_lock_held(struct kvm *kvm, bool shared)?
> 
> There are only two places that try to assert both ways as far as I can
> see on a cursory check, but it couldn't hurt.

I think there's a couple more after patches 25/26.  But there's no issue 
in having them in too (and therefore having a more complete picture) 
before figuring out what the locking API could look like.

Paolo