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Thu, 14 Nov 2024 04:02:28 -0800 (PST) X-Google-Smtp-Source: AGHT+IFwKIY5tRoZ8Bng/iyGL50AnU25kZmf3B+3O7vLZt60gMlyl0LcA6fxUzvbVVJludB/18g3KQ== X-Received: by 2002:a05:6512:39c4:b0:539:e6fc:4170 with SMTP id 2adb3069b0e04-53d9fe91a6bmr3993713e87.32.1731585747655; Thu, 14 Nov 2024 04:02:27 -0800 (PST) Received: from [192.168.10.47] ([151.49.84.243]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-432da28cad9sm21487865e9.32.2024.11.14.04.02.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Nov 2024 04:02:27 -0800 (PST) Message-ID: <70ee319f-b9ec-448a-a068-8165c8e38e6d@redhat.com> Date: Thu, 14 Nov 2024 13:02:26 +0100 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: x86: switch hugepage recovery thread to vhost_task To: Sean Christopherson Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, michael.christie@oracle.com, Tejun Heo , Luca Boccassi References: <20241108130737.126567-1-pbonzini@redhat.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/14/24 00:56, Sean Christopherson wrote: >> +static bool kvm_nx_huge_page_recovery_worker(void *data) >> +{ >> + struct kvm *kvm = data; >> long remaining_time; >> >> - while (true) { >> - start_time = get_jiffies_64(); >> - remaining_time = get_nx_huge_page_recovery_timeout(start_time); >> + if (kvm->arch.nx_huge_page_next == NX_HUGE_PAGE_DISABLED) >> + return false; > > The "next" concept is broken. Once KVM sees NX_HUGE_PAGE_DISABLED for a given VM, > KVM will never re-evaluate nx_huge_page_next. Similarly, if the recovery period > and/or ratio changes, KVM won't recompute the "next" time until the current timeout > has expired. > > I fiddled around with various ideas, but I don't see a better solution that something > along the lines of KVM's request system, e.g. set a bool to indicate the params > changed, and sprinkle smp_{r,w}mb() barriers to ensure the vhost task sees the > new params. "next" is broken, but there is a much better way to fix it. You just track the *last* time that the recovery ran. This is also better behaved when you flip recovery back and forth to disabled and back to enabled: if your recovery period is 1 minute, it will run the next recovery after 1 minute independent of how many times you flipped the parameter. This also fits much better with the "restart function after schedule()" model that vhost_task.c requires, and it gets rid of get_nx_huge_page_recovery_whatever() completely. It's also silly how close the code is to the broken v1, which is why I'm sending it below instead of sending again a large patchdd. Paolo diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 72f3bcfc54d7..e159e44a6a1b 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1444,7 +1444,7 @@ struct kvm_arch { struct kvm_x86_pmu_event_filter __rcu *pmu_event_filter; struct vhost_task *nx_huge_page_recovery_thread; - u64 nx_huge_page_next; + u64 nx_huge_page_last; #ifdef CONFIG_X86_64 /* The number of TDP MMU pages across all roots. */ diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index d0c2d9d2588f..22e7ad235123 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -7394,19 +7394,6 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm) srcu_read_unlock(&kvm->srcu, rcu_idx); } -#define NX_HUGE_PAGE_DISABLED (-1) - -static u64 get_nx_huge_page_recovery_next(void) -{ - bool enabled; - uint period; - - enabled = calc_nx_huge_pages_recovery_period(&period); - - return enabled ? get_jiffies_64() + msecs_to_jiffies(period) - : NX_HUGE_PAGE_DISABLED; -} - static void kvm_nx_huge_page_recovery_worker_kill(void *data) { } @@ -7414,12 +7401,16 @@ static void kvm_nx_huge_page_recovery_worker_kill(void *data) static bool kvm_nx_huge_page_recovery_worker(void *data) { struct kvm *kvm = data; + bool enabled; + uint period; long remaining_time; - if (kvm->arch.nx_huge_page_next == NX_HUGE_PAGE_DISABLED) + enabled = calc_nx_huge_pages_recovery_period(&period); + if (!enabled) return false; - remaining_time = kvm->arch.nx_huge_page_next - get_jiffies_64(); + remaining_time = kvm->arch.nx_huge_page_last + msecs_to_jiffies(period) + - get_jiffies_64(); if (remaining_time > 0) { schedule_timeout(remaining_time); /* check for signals and come back */ @@ -7428,7 +7419,7 @@ static bool kvm_nx_huge_page_recovery_worker(void *data) __set_current_state(TASK_RUNNING); kvm_recover_nx_huge_pages(kvm); - kvm->arch.nx_huge_page_next = get_nx_huge_page_recovery_next(); + kvm->arch.nx_huge_page_last = get_jiffies_64(); return true; } @@ -7437,11 +7428,11 @@ int kvm_mmu_post_init_vm(struct kvm *kvm) if (nx_hugepage_mitigation_hard_disabled) return 0; - kvm->arch.nx_huge_page_next = get_nx_huge_page_recovery_next(); + kvm->arch.nx_huge_page_last = get_jiffies_64(); kvm->arch.nx_huge_page_recovery_thread = vhost_task_create( kvm_nx_huge_page_recovery_worker, kvm_nx_huge_page_recovery_worker_kill, kvm, "kvm-nx-lpage-recovery"); - + if (!kvm->arch.nx_huge_page_recovery_thread) return -ENOMEM;