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KVM: KVM: Use cpumask_available() to check for NULL cpumask when kicking vCPUs

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Check for a NULL cpumask_var_t when kicking multiple vCPUs via
cpumask_available(), which performs a !NULL check if and only if cpumasks
are configured to be allocated off-stack.  This is a meaningless
optimization, e.g. avoids a TEST+Jcc and TEST+CMOV on x86, but more
importantly helps document that the NULL check is necessary even though
all callers pass in a local variable.

No functional change intended.

Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210827092516.1027264-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-08-27 11:25:10 +02:00 committed by Paolo Bonzini
parent 85b640450d
commit 0bbc2ca851
1 changed files with 15 additions and 3 deletions
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18
virt/kvm/kvm_main.c
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@ -235,9 +235,13 @@ static void ack_flush(void *_completed)
{
}
static inline bool kvm_kick_many_cpus(const struct cpumask *cpus, bool wait)
static inline bool kvm_kick_many_cpus(cpumask_var_t tmp, bool wait)
{
if (unlikely(!cpus))
const struct cpumask *cpus;
if (likely(cpumask_available(tmp)))
cpus = tmp;
else
cpus = cpu_online_mask;
if (cpumask_empty(cpus))
@ -267,6 +271,14 @@ bool kvm_make_vcpus_request_mask(struct kvm *kvm, unsigned int req,
if (!(req & KVM_REQUEST_NO_WAKEUP) && kvm_vcpu_wake_up(vcpu))
continue;
/*
* tmp can be "unavailable" if cpumasks are allocated off stack
* as allocation of the mask is deliberately not fatal and is
* handled by falling back to kicking all online CPUs.
*/
if (!cpumask_available(tmp))
continue;
/*
* Note, the vCPU could get migrated to a different pCPU at any
* point after kvm_request_needs_ipi(), which could result in
@ -278,7 +290,7 @@ bool kvm_make_vcpus_request_mask(struct kvm *kvm, unsigned int req,
* were reading SPTEs _before_ any changes were finalized. See
* kvm_vcpu_kick() for more details on handling requests.
*/
if (tmp != NULL && kvm_request_needs_ipi(vcpu, req)) {
if (kvm_request_needs_ipi(vcpu, req)) {
cpu = READ_ONCE(vcpu->cpu);
if (cpu != -1 && cpu != me)
__cpumask_set_cpu(cpu, tmp);