From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH v2 6/6] KVM: MMU: init kvm generation close to mmio wrap-around value Date: Thu, 25 Apr 2013 17:23:14 +0800 Message-ID: <5178F602.9040100@linux.vnet.ibm.com> References: <1364810209-25954-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <1364810209-25954-7-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <20130424125911.GQ12401@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: mtosatti@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org To: Gleb Natapov Return-path: In-Reply-To: <20130424125911.GQ12401@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 04/24/2013 08:59 PM, Gleb Natapov wrote: > On Mon, Apr 01, 2013 at 05:56:49PM +0800, Xiao Guangrong wrote: >> Then it has chance to trigger mmio generation number wrap-around >> >> Signed-off-by: Xiao Guangrong >> --- >> arch/x86/include/asm/kvm_host.h | 1 + >> arch/x86/kvm/mmu.c | 8 ++++++++ >> virt/kvm/kvm_main.c | 6 ++++++ >> 3 files changed, 15 insertions(+), 0 deletions(-) >> >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> index 6c1e642..4e1f7cb 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -767,6 +767,7 @@ void kvm_mmu_write_protect_pt_masked(struct kvm *kvm, >> struct kvm_memory_slot *slot, >> gfn_t gfn_offset, unsigned long mask); >> void kvm_mmu_zap_all(struct kvm *kvm); >> +void kvm_arch_init_generation(struct kvm *kvm); >> void kvm_mmu_invalid_mmio_sptes(struct kvm *kvm); >> unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm); >> void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages); >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index d314e21..dcc059c 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -4279,6 +4279,14 @@ restart: >> spin_unlock(&kvm->mmu_lock); >> } >> >> +void kvm_arch_init_generation(struct kvm *kvm) >> +{ >> + mutex_lock(&kvm->slots_lock); >> + /* It is easier to trigger mmio generation-number wrap-around. */ >> + kvm_memslots(kvm)->generation = MMIO_MAX_GEN - 13; > kvm_memslots(kvm)->generation should never overflow since > (read|write)_cached mechanism does not handle it. Initialising it to > anything but 0 makes overflow more likely. > > You can hide mmio overflow trick in kvm_current_mmio_generation(): > > static unsigned int kvm_current_mmio_generation(struct kvm *kvm) > { > return (kvm_memslots(kvm)->generation + MMIO_MAX_GEN - 13) & MMIO_GEN_MASK; > } Very smart idea. Thanks you, Gleb!