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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id v8sm4753484edc.59.2021.06.17.10.10.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Jun 2021 10:10:39 -0700 (PDT) Subject: Re: [PATCH] KVM: x86/mmu: Grab nx_lpage_splits as an unsigned long before division To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210615162905.2132937-1-seanjc@google.com> From: Paolo Bonzini Message-ID: <53476904-08ce-63ec-3842-9443a92550db@redhat.com> Date: Thu, 17 Jun 2021 19:10:38 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210615162905.2132937-1-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/06/21 18:29, Sean Christopherson wrote: > Snapshot kvm->stats.nx_lpage_splits into a local unsigned long to avoid > 64-bit division on 32-bit kernels. Casting to an unsigned long is safe > because the maximum number of shadow pages, n_max_mmu_pages, is also an > unsigned long, i.e. KVM will start recycling shadow pages before the > number of splits can exceed a 32-bit value. > > ERROR: modpost: "__udivdi3" [arch/x86/kvm/kvm.ko] undefined! > > Fixes: 7ee093d4f3f5 ("KVM: switch per-VM stats to u64") > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/mmu/mmu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 720ceb0a1f5c..7d3e57678d34 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -6043,6 +6043,7 @@ static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel > > static void kvm_recover_nx_lpages(struct kvm *kvm) > { > + unsigned long nx_lpage_splits = kvm->stat.nx_lpage_splits; > int rcu_idx; > struct kvm_mmu_page *sp; > unsigned int ratio; > @@ -6054,7 +6055,7 @@ static void kvm_recover_nx_lpages(struct kvm *kvm) > write_lock(&kvm->mmu_lock); > > ratio = READ_ONCE(nx_huge_pages_recovery_ratio); > - to_zap = ratio ? DIV_ROUND_UP(kvm->stat.nx_lpage_splits, ratio) : 0; > + to_zap = ratio ? DIV_ROUND_UP(nx_lpage_splits, ratio) : 0; > for ( ; to_zap; --to_zap) { > if (list_empty(&kvm->arch.lpage_disallowed_mmu_pages)) > break; > Queued, thanks. Paolo