From: Isaku Yamahata <isaku.yamahata@gmail.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Yuan Yao <yuan.yao@linux.intel.com>,
isaku.yamahata@intel.com, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>,
isaku.yamahata@gmail.com, Kai Huang <kai.huang@intel.com>,
Chao Gao <chao.gao@intel.com>,
Atish Patra <atishp@atishpatra.org>,
Shaokun Zhang <zhangshaokun@hisilicon.com>,
Qi Liu <liuqi115@huawei.com>, John Garry <john.garry@huawei.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Huang Ying <ying.huang@intel.com>,
Huacai Chen <chenhuacai@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH v3 10/22] KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock
Date: Tue, 6 Sep 2022 14:44:34 -0700 [thread overview]
Message-ID: <20220906214434.GA443010@ls.amr.corp.intel.com> (raw)
In-Reply-To: <87pmg9ui6h.wl-maz@kernel.org>
On Tue, Sep 06, 2022 at 07:32:22AM +0100,
Marc Zyngier <maz@kernel.org> wrote:
> On Tue, 06 Sep 2022 03:46:43 +0100,
> Yuan Yao <yuan.yao@linux.intel.com> wrote:
> >
> > On Thu, Sep 01, 2022 at 07:17:45PM -0700, isaku.yamahata@intel.com wrote:
> > > From: Isaku Yamahata <isaku.yamahata@intel.com>
> > >
> > > Because kvm_count_lock unnecessarily complicates the KVM locking convention
> > > Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock for
> > > simplicity.
> > >
> > > Opportunistically add some comments on locking.
> > >
> > > Suggested-by: Sean Christopherson <seanjc@google.com>
> > > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > > ---
> > > Documentation/virt/kvm/locking.rst | 14 +++++-------
> > > virt/kvm/kvm_main.c | 34 ++++++++++++++++++++----------
> > > 2 files changed, 28 insertions(+), 20 deletions(-)
> > >
> > > diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
> > > index 845a561629f1..8957e32aa724 100644
> > > --- a/Documentation/virt/kvm/locking.rst
> > > +++ b/Documentation/virt/kvm/locking.rst
> > > @@ -216,15 +216,11 @@ time it will be set using the Dirty tracking mechanism described above.
> > > :Type: mutex
> > > :Arch: any
> > > :Protects: - vm_list
> > > -
> > > -``kvm_count_lock``
> > > -^^^^^^^^^^^^^^^^^^
> > > -
> > > -:Type: raw_spinlock_t
> > > -:Arch: any
> > > -:Protects: - hardware virtualization enable/disable
> > > -:Comment: 'raw' because hardware enabling/disabling must be atomic /wrt
> > > - migration.
> > > + - kvm_usage_count
> > > + - hardware virtualization enable/disable
> > > +:Comment: Use cpus_read_lock() for hardware virtualization enable/disable
> > > + because hardware enabling/disabling must be atomic /wrt
> > > + migration. The lock order is cpus lock => kvm_lock.
> > >
> > > ``kvm->mn_invalidate_lock``
> > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index fc55447c4dba..082d5dbc8d7f 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -100,7 +100,6 @@ EXPORT_SYMBOL_GPL(halt_poll_ns_shrink);
> > > */
> > >
> > > DEFINE_MUTEX(kvm_lock);
> > > -static DEFINE_RAW_SPINLOCK(kvm_count_lock);
> > > LIST_HEAD(vm_list);
> > >
> > > static cpumask_var_t cpus_hardware_enabled;
> > > @@ -4996,6 +4995,8 @@ static void hardware_enable_nolock(void *caller_name)
> > > int cpu = raw_smp_processor_id();
> > > int r;
> > >
> > > + WARN_ON_ONCE(preemptible());
> >
> > This looks incorrect, it may triggers everytime when online CPU.
> > Because patch 7 moved CPUHP_AP_KVM_STARTING *AFTER*
> > CPUHP_AP_ONLINE_IDLE as CPUHP_AP_KVM_ONLINE, then cpuhp_thread_fun()
> > runs the new CPUHP_AP_KVM_ONLINE in *non-atomic* context:
> >
> > cpuhp_thread_fun(unsigned int cpu) {
> > ...
> > if (cpuhp_is_atomic_state(state)) {
> > local_irq_disable();
> > st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
> > local_irq_enable();
> >
> > WARN_ON_ONCE(st->result);
> > } else {
> > st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
> > }
> > ...
> > }
> >
> > static bool cpuhp_is_atomic_state(enum cpuhp_state state)
> > {
> > return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
> > }
> >
> > The hardware_enable_nolock() now is called in 2 cases:
> > 1. in atomic context by on_each_cpu().
> > 2. From non-atomic context by CPU hotplug thread.
> >
> > so how about "WARN_ONCE(preemptible() && cpu_active(cpu))" ?
>
> I suspect similar changes must be applied to the arm64 side (though
> I'm still looking for a good definition of cpu_active()).
It seems plausible. I tested cpu online/offline on x86. Let me update arm64 code
too.
--
Isaku Yamahata <isaku.yamahata@gmail.com>
next prev parent reply other threads:[~2022-09-06 21:44 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-02 2:17 [PATCH v3 00/22] KVM: hardware enable/disable reorganize isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 01/22] KVM: x86: Drop kvm_user_return_msr_cpu_online() isaku.yamahata
2022-09-05 1:59 ` Chao Gao
2022-09-05 5:30 ` Yuan Yao
2022-09-02 2:17 ` [PATCH v3 02/22] KVM: x86: Use this_cpu_ptr() instead of per_cpu_ptr(smp_processor_id()) isaku.yamahata
2022-09-05 5:35 ` Yuan Yao
2022-09-02 2:17 ` [PATCH v3 03/22] KVM: x86: Move check_processor_compatibility from init ops to runtime ops isaku.yamahata
2022-09-05 5:42 ` Yuan Yao
2022-09-02 2:17 ` [PATCH v3 04/22] Partially revert "KVM: Pass kvm_init()'s opaque param to additional arch funcs" isaku.yamahata
2022-09-05 5:48 ` Yuan Yao
2022-09-02 2:17 ` [PATCH v3 05/22] KVM: Provide more information in kernel log if hardware enabling fails isaku.yamahata
2022-09-05 5:56 ` Yuan Yao
2022-09-02 2:17 ` [PATCH v3 06/22] KVM: arm64: Simplify the CPUHP logic isaku.yamahata
2022-09-05 7:05 ` Yuan Yao
2022-09-05 9:29 ` Marc Zyngier
2022-09-05 12:39 ` Marc Zyngier
2022-09-07 15:12 ` Isaku Yamahata
2022-09-02 2:17 ` [PATCH v3 07/22] KVM: Rename and move CPUHP_AP_KVM_STARTING to ONLINE section isaku.yamahata
2022-09-05 7:49 ` Yuan Yao
2022-09-02 2:17 ` [PATCH v3 08/22] KVM: Do compatibility checks on hotplugged CPUs isaku.yamahata
2022-09-06 1:25 ` Yuan Yao
2022-09-02 2:17 ` [PATCH v3 09/22] KVM: Do processor compatibility check on resume isaku.yamahata
2022-09-05 8:40 ` Yuan Yao
2022-09-05 9:27 ` Yuan Yao
2022-09-08 18:21 ` Isaku Yamahata
2022-09-02 2:17 ` [PATCH v3 10/22] KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock isaku.yamahata
2022-09-06 2:46 ` Yuan Yao
2022-09-06 6:32 ` Marc Zyngier
2022-09-06 21:44 ` Isaku Yamahata [this message]
2022-09-08 18:24 ` Isaku Yamahata
2022-09-02 2:17 ` [PATCH v3 11/22] KVM: Add arch hooks for PM events with empty stub isaku.yamahata
2022-09-06 6:25 ` Yuan Yao
2022-09-08 19:11 ` Isaku Yamahata
2022-09-02 2:17 ` [PATCH v3 12/22] KVM: x86: Move TSC fixup logic to KVM arch resume callback isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 13/22] KVM: Add arch hook when VM is added/deleted isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 14/22] KVM: Move out KVM arch PM hooks and hardware enable/disable logic isaku.yamahata
2022-09-06 7:43 ` Yuan Yao
2022-09-08 19:15 ` Isaku Yamahata
2022-09-02 2:17 ` [PATCH v3 15/22] KVM: kvm_arch.c: Remove _nolock post fix isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 16/22] KVM: kvm_arch.c: Remove a global variable, hardware_enable_failed isaku.yamahata
2022-09-07 5:56 ` Yuan Yao
2022-09-08 22:51 ` Isaku Yamahata
2022-09-02 2:17 ` [PATCH v3 17/22] KVM: x86: Duplicate arch callbacks related to pm events isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 18/22] KVM: Eliminate kvm_arch_post_init_vm() isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 19/22] KVM: x86: Delete kvm_arch_hardware_enable/disable() isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 20/22] KVM: Add config to not compile kvm_arch.c isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 21/22] RFC: KVM: x86: Remove cpus_hardware_enabled and related sanity check isaku.yamahata
2022-09-02 2:17 ` [PATCH v3 22/22] RFC: KVM: " isaku.yamahata
2022-09-05 15:38 ` [PATCH v3 00/22] KVM: hardware enable/disable reorganize Marc Zyngier
2022-09-06 22:25 ` Isaku Yamahata
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