Messages in this thread Patch in this message | | | Date | Fri, 20 Aug 2021 17:05:01 -0700 | Subject | [PATCH 2/2] KVM: Guard cpusmask NULL check with CONFIG_CPUMASK_OFFSTACK | From | Sean Christopherson <> |
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Check for a NULL cpumask_var_t when kicking multiple vCPUs 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.
Signed-off-by: Sean Christopherson <seanjc@google.com> --- virt/kvm/kvm_main.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 786b914db98f..82c5280dd5ce 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -247,7 +247,7 @@ static void ack_flush(void *_completed) static inline bool kvm_kick_many_cpus(const struct cpumask *cpus, bool wait) { - if (unlikely(!cpus)) + if (IS_ENABLED(CONFIG_CPUMASK_OFFSTACK) && unlikely(!cpus)) cpus = cpu_online_mask; if (cpumask_empty(cpus)) @@ -277,6 +277,14 @@ 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 NULL 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 (IS_ENABLED(CONFIG_CPUMASK_OFFSTACK) && !tmp) + continue; + /* * Note, the vCPU could get migrated to a different pCPU at any * point after kvm_request_needs_ipi(), which could result in @@ -288,7 +296,7 @@ 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); -- 2.33.0.rc2.250.ged5fa647cd-goog
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