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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id i16sm6484337wrq.73.2020.09.04.02.53.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2020 02:53:34 -0700 (PDT) From: Vitaly Kuznetsov To: Haiwei Li Cc: "pbonzini\@redhat.com" , Sean Christopherson , "wanpengli\@tencent.com" , "jmattson\@google.com" , "joro\@8bytes.org" , tglx@linutronix.de, mingo@redhat.com, "bp\@alien8.de" , "hpa\@zytor.com" , "linux-kernel\@vger.kernel.org" , "kvm\@vger.kernel.org" , "x86\@kernel.org" Subject: Re: [PATCH v2] KVM: Check the allocation of pv cpu mask In-Reply-To: <61e2fd6f-effd-64d7-148a-1b1f9fda1449@gmail.com> References: <654d8c60-49f0-e398-be25-24aed352360d@gmail.com> <87y2lrnnyf.fsf@vitty.brq.redhat.com> <61e2fd6f-effd-64d7-148a-1b1f9fda1449@gmail.com> Date: Fri, 04 Sep 2020 11:53:33 +0200 Message-ID: <87o8mlooki.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Haiwei Li writes: > On 20/9/3 18:39, Vitaly Kuznetsov wrote: >> Haiwei Li writes: >> >>> From: Haiwei Li >>> >>> check the allocation of per-cpu __pv_cpu_mask. Initialize ops only when >>> successful. >>> >>> Signed-off-by: Haiwei Li >>> --- >>> arch/x86/kernel/kvm.c | 24 ++++++++++++++++++++---- >>> 1 file changed, 20 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c >>> index 08320b0b2b27..d3c062e551d7 100644 >>> --- a/arch/x86/kernel/kvm.c >>> +++ b/arch/x86/kernel/kvm.c >>> @@ -555,7 +555,6 @@ static void kvm_send_ipi_mask_allbutself(const >>> struct cpumask *mask, int vector) >>> static void kvm_setup_pv_ipi(void) >>> { >>> apic->send_IPI_mask = kvm_send_ipi_mask; >>> - apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself; >>> pr_info("setup PV IPIs\n"); >>> } >>> >>> @@ -654,7 +653,6 @@ static void __init kvm_guest_init(void) >>> } >>> >>> if (pv_tlb_flush_supported()) { >>> - pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others; >>> pv_ops.mmu.tlb_remove_table = tlb_remove_table; >>> pr_info("KVM setup pv remote TLB flush\n"); >>> } >>> @@ -767,6 +765,14 @@ static __init int activate_jump_labels(void) >>> } >>> arch_initcall(activate_jump_labels); >>> >>> +static void kvm_free_pv_cpu_mask(void) >>> +{ >>> + unsigned int cpu; >>> + >>> + for_each_possible_cpu(cpu) >>> + free_cpumask_var(per_cpu(__pv_cpu_mask, cpu)); >>> +} >>> + >>> static __init int kvm_alloc_cpumask(void) >>> { >>> int cpu; >>> @@ -785,11 +791,21 @@ static __init int kvm_alloc_cpumask(void) >>> >>> if (alloc) >>> for_each_possible_cpu(cpu) { >>> - zalloc_cpumask_var_node(per_cpu_ptr(&__pv_cpu_mask, cpu), >>> - GFP_KERNEL, cpu_to_node(cpu)); >>> + if (!zalloc_cpumask_var_node( >>> + per_cpu_ptr(&__pv_cpu_mask, cpu), >>> + GFP_KERNEL, cpu_to_node(cpu))) >>> + goto zalloc_cpumask_fail; >>> } >>> >>> +#if defined(CONFIG_SMP) >>> + apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself; >>> +#endif >>> + pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others; >> >> This is too late I'm afraid. If I'm not mistaken PV patching happens >> earlier, so .init.guest_late_init (kvm_guest_init()) is good and >> arch_initcall() is bad. > > .init.guest_late_init (kvm_guest_init()) is called before > arch_initcall() and kvm_flush_tlb_others && kvm_send_ipi_mask_allbutself > rely on __pv_cpu_mask. So, i can not put this assign in kvm_guest_init(). > >> >> Have you checked that with this patch kvm_flush_tlb_others() is still >> being called? > > yes. I add a printk and i get the log. > This is weird. I do the following on top of your patch: diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index d3c062e551d7..f441209ff0a4 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -620,6 +620,8 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask, struct kvm_steal_time *src; struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask); + trace_printk("PV TLB flush %d CPUs\n", cpumask_weight(cpumask)); + cpumask_copy(flushmask, cpumask); /* * We have to call flush only on online vCPUs. And With your patch I don't see any calls: # grep -c -v '^#' /sys/kernel/debug/tracing/trace 0 with your patch reverted I see them: # grep -c -v '^#' /sys/kernel/debug/tracing/trace 4571 >> >> Actually, there is no need to assign kvm_flush_tlb_others() so late. We >> can always check if __pv_cpu_mask was allocated and revert back to the >> architectural path if not. > I am sorry i don't really understand. Can you explain in more detail? Thx. > I mean we can always call e.g. kvm_flush_tlb_others(), even if (very unlikely) the mask wasn't allocated. We just need to check for that. Something like (completely untested): diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index d3c062e551d7..e3676cdee6a2 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -620,6 +620,11 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask, struct kvm_steal_time *src; struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask); + if (unlikely(!flushmask)) { + flushmask = cpumask; + goto do_native; + } + cpumask_copy(flushmask, cpumask); /* * We have to call flush only on online vCPUs. And @@ -635,6 +640,7 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask, } } +do_native: native_flush_tlb_others(flushmask, info); } >> >>> return 0; >>> + >>> +zalloc_cpumask_fail: >>> + kvm_free_pv_cpu_mask(); >>> + return -ENOMEM; >>> } >>> arch_initcall(kvm_alloc_cpumask); >>> >>> -- >>> 2.18.4 >>> >> > -- Vitaly