KVM: PPC: Book3S HV: Fix decrementer timeouts with non-zero TB offset

Commit c7699822bc21 ("KVM: PPC: Book3S HV: Make physical thread 0 do
the MMU switching") reordered the guest entry/exit code so that most
of the guest register save/restore code happened in guest MMU context.
A side effect of that is that the timebase still contains the guest
timebase value at the point where we compute and use vcpu->arch.dec_expires,
and therefore that is now a guest timebase value rather than a host
timebase value.  That in turn means that the timeouts computed in
kvmppc_set_timer() are wrong if the timebase offset for the guest is
non-zero.  The consequence of that is things such as "sleep 1" in a
guest after migration may sleep for much longer than they should.

This fixes the problem by converting between guest and host timebase
values as necessary, by adding or subtracting the timebase offset.
This also fixes an incorrect comment.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Scott Wood <scottwood@freescale.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 61190ddd9f3b..42bd2e694b1b 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -841,6 +841,10 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
          * Set the decrementer to the guest decrementer.
          */
         ld      r8,VCPU_DEC_EXPIRES(r4)
+        /* r8 is a host timebase value here, convert to guest TB */
+        ld      r5,HSTATE_KVM_VCORE(r13)
+        ld      r6,VCORE_TB_OFFSET(r5)
+        add     r8,r8,r6
         mftb    r7
         subf    r3,r7,r8
         mtspr   SPRN_DEC,r3
@@ -1204,6 +1208,10 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_201)
         mftb    r6
         extsw   r5,r5
         add     r5,r5,r6
+        /* r5 is a guest timebase value here, convert to host TB */
+        ld      r3,HSTATE_KVM_VCORE(r13)
+        ld      r4,VCORE_TB_OFFSET(r3)
+        subf    r5,r4,r5
         std     r5,VCPU_DEC_EXPIRES(r9)
 
 BEGIN_FTR_SECTION
@@ -1479,7 +1487,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
         ld      r8,VCORE_TB_OFFSET(r5)
         cmpdi   r8,0
         beq     17f
-        mftb    r6                      /* current host timebase */
+        mftb    r6                      /* current guest timebase */
         subf    r8,r8,r6
         mtspr   SPRN_TBU40,r8           /* update upper 40 bits */
         mftb    r7                      /* check if lower 24 bits overflowed */