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[34.82.80.254]) by smtp.gmail.com with ESMTPSA id mg17sm459179pjb.17.2021.11.29.16.50.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Nov 2021 16:50:56 -0800 (PST) Date: Tue, 30 Nov 2021 00:50:53 +0000 From: David Matlack To: Mingwei Zhang Cc: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon Subject: Re: [PATCH 1/2] Revert "KVM: x86/mmu: Don't step down in the TDP iterator when zapping all SPTEs" Message-ID: References: <20211124214421.458549-1-mizhang@google.com> <20211124214421.458549-2-mizhang@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211124214421.458549-2-mizhang@google.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Nov 24, 2021 at 09:44:20PM +0000, Mingwei Zhang wrote: > Not stepping down in TDP iterator in `zap_all` case avoids re-reading the > non-leaf SPTEs, thus accelerates the zapping process . But when the number > of SPTEs is too large, we may run out of CPU time and causes a RCU stall > warnings in __handle_changed_pte() in the context of zap_gfn_range(). > > Revert this patch to allow eliminating RCU stall warning using a two-phase > zapping for `zap_all` case. > > This reverts commit 0103098fb4f13b447b26ed514bcd3140f6791047. > > Cc: Sean Christopherson > Cc: Ben Gardon > Cc: David Matlack > > Signed-off-by: Mingwei Zhang Reviewed-by: David Matlack > --- > arch/x86/kvm/mmu/tdp_mmu.c | 9 +-------- > 1 file changed, 1 insertion(+), 8 deletions(-) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 7c5dd83e52de..89d16bb104de 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -706,12 +706,6 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > bool zap_all = (start == 0 && end >= max_gfn_host); > struct tdp_iter iter; > > - /* > - * No need to try to step down in the iterator when zapping all SPTEs, > - * zapping the top-level non-leaf SPTEs will recurse on their children. > - */ > - int min_level = zap_all ? root->role.level : PG_LEVEL_4K; > - > /* > * Bound the walk at host.MAXPHYADDR, guest accesses beyond that will > * hit a #PF(RSVD) and never get to an EPT Violation/Misconfig / #NPF, > @@ -723,8 +717,7 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > > rcu_read_lock(); > > - for_each_tdp_pte_min_level(iter, root->spt, root->role.level, > - min_level, start, end) { > + tdp_root_for_each_pte(iter, root, start, end) { > retry: > if (can_yield && > tdp_mmu_iter_cond_resched(kvm, &iter, flush, shared)) { > -- > 2.34.0.rc2.393.gf8c9666880-goog >