linux-kernel - [PATCH 5.16 0905/1017] KVM: x86: fix sending PV IPI

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Date:   Tue,  5 Apr 2022 09:30:18 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Li RongQing <lirongqing@...du.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.16 0905/1017] KVM: x86: fix sending PV IPI

From: Li RongQing <lirongqing@...du.com>

commit c15e0ae42c8e5a61e9aca8aac920517cf7b3e94e upstream.

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@...du.com>
Message-Id: <1646814944-51801-1-git-send-email-lirongqing@...du.com>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/kvm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -515,7 +515,7 @@ static void __send_ipi_mask(const struct
 		} 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,