linux-kernel - Re: [PATCH v2 22/28] KVM: x86/mmu: Mark SPTEs in disconnected pages as removed

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Message-ID: <cb7108c7-e4f2-ea59-24f4-7c7da45054a8@redhat.com>
Date:   Wed, 3 Feb 2021 12:17:21 +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 22/28] KVM: x86/mmu: Mark SPTEs in disconnected pages
 as removed

On 02/02/21 19:57, Ben Gardon wrote:
> 
> +			 * Marking the SPTE as a removed SPTE is not
> +			 * strictly necessary here as the MMU lock should

"should" is a bit too weak---the point of !shared is that the MMU lock 
*will* stop other threads from concurrent modifications of the SPTEs.

Paolo

> +			 * stop other threads from concurrentrly modifying
> +			 * this SPTE. Using the removed SPTE value keeps
> +			 * the shared and non-atomic cases consistent and
> +			 * simplifies the function.
> +			 */
> +			WRITE_ONCE(*sptep, REMOVED_SPTE);