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KVM: Disable CPU hotplug during hardware enabling/disabling

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Disable CPU hotplug when enabling/disabling hardware to prevent the
corner case where if the following sequence occurs:

  1. A hotplugged CPU marks itself online in cpu_online_mask
  2. The hotplugged CPU enables interrupt before invoking KVM's ONLINE
     callback
  3  hardware_{en,dis}able_all() is invoked on another CPU

the hotplugged CPU will be included in on_each_cpu() and thus get sent
through hardware_{en,dis}able_nolock() before kvm_online_cpu() is called.

        start_secondary { ...
                set_cpu_online(smp_processor_id(), true); <- 1
                ...
                local_irq_enable();  <- 2
                ...
                cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); <- 3
        }

KVM currently fudges around this race by keeping track of which CPUs have
done hardware enabling (see commit 1b6c016818 "KVM: Keep track of which
cpus have virtualization enabled"), but that's an inefficient, convoluted,
and hacky solution.

Signed-off-by: Chao Gao <chao.gao@intel.com>
[sean: split to separate patch, write changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-43-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Chao Gao 2022-11-30 23:09:26 +00:00 • committed by Paolo Bonzini
parent aaf12a7b43
commit e4aa7f88af
2 changed files with 22 additions and 1 deletions
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11
arch/x86/kvm/x86.c
View file

@ -9296,7 +9296,16 @@ static inline void kvm_ops_update(struct kvm_x86_init_ops *ops)
static int kvm_x86_check_processor_compatibility(void)
{
struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
int cpu = smp_processor_id();
struct cpuinfo_x86 *c = &cpu_data(cpu);
/*
* Compatibility checks are done when loading KVM and when enabling
* hardware, e.g. during CPU hotplug, to ensure all online CPUs are
* compatible, i.e. KVM should never perform a compatibility check on
* an offline CPU.
*/
WARN_ON(!cpu_online(cpu));
if (__cr4_reserved_bits(cpu_has, c) !=
__cr4_reserved_bits(cpu_has, &boot_cpu_data))

12
virt/kvm/kvm_main.c
View file

@ -5167,15 +5167,26 @@ static void hardware_disable_all_nolock(void)
static void hardware_disable_all(void)
{
cpus_read_lock();
raw_spin_lock(&kvm_count_lock);
hardware_disable_all_nolock();
raw_spin_unlock(&kvm_count_lock);
cpus_read_unlock();
}
static int hardware_enable_all(void)
{
int r = 0;
/*
* When onlining a CPU, cpu_online_mask is set before kvm_online_cpu()
* is called, and so on_each_cpu() between them includes the CPU that
* is being onlined. As a result, hardware_enable_nolock() may get
* invoked before kvm_online_cpu(), which also enables hardware if the
* usage count is non-zero. Disable CPU hotplug to avoid attempting to
* enable hardware multiple times.
*/
cpus_read_lock();
raw_spin_lock(&kvm_count_lock);
kvm_usage_count++;
@ -5190,6 +5201,7 @@ static int hardware_enable_all(void)
}
raw_spin_unlock(&kvm_count_lock);
cpus_read_unlock();
return r;
}