From: Sean Christopherson <seanjc@google.com>
To: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Igor Mammedov <imammedo@redhat.com>,
Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Huacai Chen <chenhuacai@kernel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
Paul Mackerras <paulus@ozlabs.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
David Hildenbrand <david@redhat.com>,
Cornelia Huck <cohuck@redhat.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 01/13] KVM: x86: Cache total page count to avoid traversing the memslot array
Date: Wed, 20 Oct 2021 19:01:51 +0000 [thread overview]
Message-ID: <YXBnn6ZaXbaqKvOo@google.com> (raw)
In-Reply-To: <e618edce-b310-6d9a-3860-d7f4d8c0d98f@maciej.szmigiero.name>
On Wed, Oct 20, 2021, Maciej S. Szmigiero wrote:
> On 20.10.2021 00:24, Sean Christopherson wrote:
> > E.g. the whole thing can be
> >
> > if (!kvm->arch.n_requested_mmu_pages &&
> > (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
> > unsigned long nr_mmu_pages;
> >
> > if (change == KVM_MR_CREATE) {
> > kvm->arch.n_memslots_pages += new->npages;
> > } else {
> > WARN_ON(kvm->arch.n_memslots_pages < old->npages);
> > kvm->arch.n_memslots_pages -= old->npages;
> > }
> >
> > nr_mmu_pages = (unsigned long)kvm->arch.n_memslots_pages;
> > nr_mmu_pages *= (KVM_PERMILLE_MMU_PAGES / 1000);
>
> The above line will set nr_mmu_pages to zero since KVM_PERMILLE_MMU_PAGES
> is 20, so when integer-divided by 1000 will result in a multiplication
> coefficient of zero.
Ugh, math. And thus do_div() to avoid the whole 64-bit divide issue on 32-bit KVM.
Bummer.
next prev parent reply other threads:[~2021-10-20 19:02 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 21:38 [PATCH v5 00/13] KVM: Scalable memslots implementation Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 01/13] KVM: x86: Cache total page count to avoid traversing the memslot array Maciej S. Szmigiero
2021-10-19 22:24 ` Sean Christopherson
2021-10-19 22:31 ` Sean Christopherson
2021-10-20 18:40 ` Maciej S. Szmigiero
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-10-20 19:01 ` Sean Christopherson [this message]
2021-11-01 22:29 ` Sean Christopherson
2021-11-03 11:59 ` Maciej S. Szmigiero
2021-11-03 14:47 ` Sean Christopherson
2021-11-03 15:38 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 02/13] KVM: x86: Don't call kvm_mmu_change_mmu_pages() if the count hasn't changed Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 03/13] KVM: Add "old" memslot parameter to kvm_arch_prepare_memory_region() Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 04/13] KVM: x86: Move n_memslots_pages recalc " Maciej S. Szmigiero
2021-10-19 22:38 ` Sean Christopherson
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 05/13] KVM: Integrate gfn_to_memslot_approx() into search_memslots() Maciej S. Szmigiero
2021-10-19 23:38 ` Sean Christopherson
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 06/13] KVM: Move WARN on invalid memslot index to update_memslots() Maciej S. Szmigiero
2021-10-19 23:42 ` Sean Christopherson
2021-09-20 21:38 ` [PATCH v5 07/13] KVM: Just resync arch fields when slots_arch_lock gets reacquired Maciej S. Szmigiero
2021-10-19 23:55 ` Sean Christopherson
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-10-20 18:57 ` Sean Christopherson
2021-10-20 18:58 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 08/13] KVM: Resolve memslot ID via a hash table instead of via a static array Maciej S. Szmigiero
2021-10-20 0:43 ` Sean Christopherson
2021-10-20 18:42 ` Maciej S. Szmigiero
2021-10-20 22:39 ` Sean Christopherson
2021-10-21 14:15 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 09/13] KVM: Use interval tree to do fast hva lookup in memslots Maciej S. Szmigiero
2021-10-26 18:19 ` Sean Christopherson
2021-10-26 18:46 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 10/13] KVM: s390: Introduce kvm_s390_get_gfn_end() Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 11/13] KVM: Keep memslots in tree-based structures instead of array-based ones Maciej S. Szmigiero
2021-10-27 0:36 ` Sean Christopherson
2021-10-27 23:54 ` Sean Christopherson
2021-10-28 22:22 ` Sean Christopherson
2021-09-20 21:39 ` [PATCH v5 12/13] KVM: Optimize gfn lookup in kvm_zap_gfn_range() Maciej S. Szmigiero
2021-10-20 23:47 ` Sean Christopherson
2021-10-21 14:16 ` Maciej S. Szmigiero
2021-10-21 16:30 ` Sean Christopherson
2021-10-21 21:44 ` Maciej S. Szmigiero
2021-09-20 21:39 ` [PATCH v5 13/13] KVM: Optimize overlapping memslots check Maciej S. Szmigiero
2021-10-26 18:59 ` Sean Christopherson
2021-10-27 13:48 ` Maciej S. Szmigiero
2021-10-28 17:53 ` Sean Christopherson
2021-10-29 16:23 ` Maciej S. Szmigiero
2021-10-30 0:32 ` Sean Christopherson
2021-10-19 22:07 ` [PATCH v5 00/13] KVM: Scalable memslots implementation Sean Christopherson
2021-10-20 18:40 ` Maciej S. Szmigiero
2021-10-20 19:58 ` Sean Christopherson
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