KVM: x86: fix sending PV IPI

If apic_id is less than min, and (max - apic_id) is greater than
KVM_IPI_CLUSTER_SIZE, then the third check condition is satisfied but
the new apic_id does not fit the bitmask.  In this case __send_ipi_mask
should send the IPI.

This is mostly theoretical, but it can happen if the apic_ids on three
iterations of the loop are for example 1, KVM_IPI_CLUSTER_SIZE, 0.

Fixes: aaffcfd1e82 ("KVM: X86: Implement PV IPIs in linux guest")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Message-Id: <1646814944-51801-1-git-send-email-lirongqing@baidu.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index d77481e..ed8a13a 100644 (file)
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -517,7 +517,7 @@ static void __send_ipi_mask(const struct cpumask *mask, int vector)
                } else if (apic_id < min && max - apic_id < KVM_IPI_CLUSTER_SIZE) {
                        ipi_bitmap <<= min - apic_id;
                        min = apic_id;
-               } else if (apic_id < min + KVM_IPI_CLUSTER_SIZE) {
+               } else if (apic_id > min && apic_id < min + KVM_IPI_CLUSTER_SIZE) {
                        max = apic_id < max ? max : apic_id;
                } else {
                        ret = kvm_hypercall4(KVM_HC_SEND_IPI, (unsigned long)ipi_bitmap,