KVM: PPC: Book3S HV: Avoid unbalanced increments of VPA yield count

The yield count in the VPA is supposed to be incremented every time
we enter the guest, and every time we exit the guest, so that its
value is even when the vcpu is running in the guest and odd when it
isn't.  However, it's currently possible that we increment the yield
count on the way into the guest but then find that other CPU threads
are already exiting the guest, so we go back to nap mode via the
secondary_too_late label.  In this situation we don't increment the
yield count again, breaking the relationship between the LSB of the
count and whether the vcpu is in the guest.

To fix this, we move the increment of the yield count to a point
after we have checked whether other CPU threads are exiting.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index c91ae2b..0effcd1 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -405,16 +405,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
        /* Save R1 in the PACA */
        std     r1, HSTATE_HOST_R1(r13)
 
-       /* Increment yield count if they have a VPA */
-       ld      r3, VCPU_VPA(r4)
-       cmpdi   r3, 0
-       beq     25f
-       lwz     r5, LPPACA_YIELDCOUNT(r3)
-       addi    r5, r5, 1
-       stw     r5, LPPACA_YIELDCOUNT(r3)
-       li      r6, 1
-       stb     r6, VCPU_VPA_DIRTY(r4)
-25:
        /* Load up DAR and DSISR */
        ld      r5, VCPU_DAR(r4)
        lwz     r6, VCPU_DSISR(r4)
@@ -525,6 +515,16 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201)
        mtspr   SPRN_RMOR,r8
        isync
 
+       /* Increment yield count if they have a VPA */
+       ld      r3, VCPU_VPA(r4)
+       cmpdi   r3, 0
+       beq     25f
+       lwz     r5, LPPACA_YIELDCOUNT(r3)
+       addi    r5, r5, 1
+       stw     r5, LPPACA_YIELDCOUNT(r3)
+       li      r6, 1
+       stb     r6, VCPU_VPA_DIRTY(r4)
+25:
        /* Check if HDEC expires soon */
        mfspr   r3,SPRN_HDEC
        cmpwi   r3,10