The use of smp_call_function_many() in kvm_emulate_wbinvd_noskip()

[Nadav Amit <nadav.amit@xxxxxxxxx>]

KVM is none of my business these days, but I was reviewing the use of
smp_call_function_many(), as I made some changes to related code. During
this review, I was looking at kvm_emulate_wbinvd_noskip(), and it seems wrong
to me.

As you may or might now know, smp_call_function_many() does not execute the
provided function on the local core. Considering this behavior, I am not sure
the behavior of kvm_emulate_wbinvd_noskip() is correct. IIUC, there is an
expectation that wbinvd_ipi() would run on the local core, but it would not.

If this behavior is wrong, consider using on_each_cpu_mask() instead
of smp_call_function_many().

To be fair, I guess do not understand the code too well, since it really
looks all racy to me (clearing wbinvd_dirty_mask instead of clearing local
CPU from wbinvd_ipi()).


static int kvm_emulate_wbinvd_noskip(struct kvm_vcpu *vcpu)
{
        if (!need_emulate_wbinvd(vcpu))   
                return X86EMUL_CONTINUE;  

        if (static_call(kvm_x86_has_wbinvd_exit)()) {
                int cpu = get_cpu();      

                cpumask_set_cpu(cpu, vcpu->arch.wbinvd_dirty_mask);
                smp_call_function_many(vcpu->arch.wbinvd_dirty_mask,
                                wbinvd_ipi, NULL, 1);
                put_cpu();                
                cpumask_clear(vcpu->arch.wbinvd_dirty_mask);
        } else
                wbinvd();                 
        return X86EMUL_CONTINUE;          
}