From 0bbc2ca8515f9cdf11df84ccb63dc7c44bc3d8f4 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 27 Aug 2021 11:25:10 +0200 Subject: KVM: KVM: Use cpumask_available() to check for NULL cpumask when kicking vCPUs 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 Signed-off-by: Sean Christopherson Signed-off-by: Vitaly Kuznetsov Message-Id: <20210827092516.1027264-3-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) (limited to 'virt') diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 490c8cb8cc8d..e95e7a9e4d53 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -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); -- cgit