[PATCH v2 18/30] KVM: MIPS/TLB: Fix off-by-one in TLB invalidate

[James Hogan <james.hogan@imgtec.com>]

kvm_mips_host_tlb_inv() uses the TLBP instruction to probe the host TLB
for an entry matching the given guest virtual address, and determines
whether a match was found based on whether CP0_Index > 0. This is
technically incorrect as an index of 0 (with the high bit clear) is a
perfectly valid TLB index.

This is harmless at the moment due to the use of at least 1 wired TLB
entry for the KVM commpage, however we will soon be ridding ourselves of
that particular wired entry so lets fix the condition in case the entry
needing invalidation does land at TLB index 0.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
---
 arch/mips/kvm/tlb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kvm/tlb.c b/arch/mips/kvm/tlb.c
index 6c1f894b8754..4bf82613d440 100644
--- a/arch/mips/kvm/tlb.c
+++ b/arch/mips/kvm/tlb.c
@@ -282,7 +282,7 @@ int kvm_mips_host_tlb_inv(struct kvm_vcpu *vcpu, unsigned long va)
 	if (idx >= current_cpu_data.tlbsize)
 		BUG();
 
-	if (idx > 0) {
+	if (idx >= 0) {
 		write_c0_entryhi(UNIQUE_ENTRYHI(idx));
 		write_c0_entrylo0(0);
 		write_c0_entrylo1(0);
@@ -297,7 +297,7 @@ int kvm_mips_host_tlb_inv(struct kvm_vcpu *vcpu, unsigned long va)
 
 	local_irq_restore(flags);
 
-	if (idx > 0)
+	if (idx >= 0)
 		kvm_debug("%s: Invalidated entryhi %#lx @ idx %d\n", __func__,
 			  (va & VPN2_MASK) | kvm_mips_get_user_asid(vcpu), idx);
 
-- 
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