linux-kernel - Re: [PATCH v3 7/8] KVM: x86/mmu: Protect rmaps independently with SRCU

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Date:   Tue, 11 May 2021 18:45:59 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Peter Xu <peterx@...hat.com>, Peter Shier <pshier@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>
Subject: Re: [PATCH v3 7/8] KVM: x86/mmu: Protect rmaps independently with
 SRCU

On 11/05/21 18:22, Ben Gardon wrote:
>> Yes, and I'm arguing that annotating the rmaps as __rcu is wrong because they
>> themselves are not protected by SRCU.  The memslot that contains the rmaps is
>> protected by SRCU, and because of that asserting SRCU is held for read will hold
>> true.  But, if the memslot code were changed to use a different protection scheme,
>> e.g. a rwlock for argument's sake, then the SRCU assertion would fail even though
>> the rmap logic itself didn't change.
>
> I'm inclined to agree with Sean that the extra RCU annotations are
> probably unnecessary since we're already doing the srcu dereference
> for all the slots. I'll move all these RCU annotations to their own
> patch and put it at the end of the series when I send v4.
> 

Fair enough, you can even remove them then.

Paolo