Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 21 Oct 2021 17:09:29 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     David Matlack <dmatlack@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Suleiman Souhlal <suleiman@google.com>,
        kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: Re: [PATCHV2 1/3] KVM: x86: introduce kvm_mmu_pte_prefetch structure
Message-ID: <YXEgOf1JzTmdRP6u@google.com>
References: <20211019153214.109519-1-senozhatsky@chromium.org>
 <20211019153214.109519-2-senozhatsky@chromium.org>
 <CALzav=cLXXZYBSH6iJifkqVijLAU5EvgVg2W4HKhqke2JBa+yg@mail.gmail.com>
 <YW9vqgwU+/iVooXj@google.com>
 <CALzav=c1LXXWSi-Z0_X35HCyQtv1rh0p2YmJ289J51SHy0DRxg@mail.gmail.com>
 <YXDU/xXkWGuDJ/id@google.com>
 <YXDeRej39voc7lJU@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YXDeRej39voc7lJU@google.com>
Precedence: bulk

On (21/10/21 12:28), Sergey Senozhatsky wrote:
> > 
> > We are using TDP. And somehow I never see (literally never) async PFs.
> > It's always either hva_to_pfn_fast() or hva_to_pfn_slow() or
> > __direct_map() from tdp_page_fault().
> 
> Hmm, and tdp_page_fault()->fast_page_fault() always fails on
> !is_access_allowed(error_code, new_spte), it never handles the faults.
> And I see some ->mmu_lock contention:
> 
> 	spin_lock(&vcpu->kvm->mmu_lock);
> 	__direct_map();
> 	spin_unlock(&vcpu->kvm->mmu_lock);
> 
> So it might be that we setup guest memory wrongly and never get
> advantages of TPD and fast page faults?

No, never mind, that's probably expected and ->mmu_lock contention is not
severe.