KVM: PPC: Book3S HV: Fix guest r11 corruption with POWER9 TM workarounds

When we come into the softpatch handler (0x1500), we use r11 to store
the HSRR0 for later use by the denorm handler.

We also use the softpatch handler for the TM workarounds for
POWER9. Unfortunately, in kvmppc_interrupt_hv we later store r11 out
to the vcpu assuming it's still what we got from userspace.

This causes r11 to be corrupted in the VCPU and hence when we restore
the guest, we get a corrupted r11. We've seen this when running TM
tests inside guests on P9.

This fixes the problem by only touching r11 in the denorm case.

Fixes: 4bb3c7a020 ("KVM: PPC: Book3S HV: Work around transactional memory bugs in POWER9")
Cc: <stable@vger.kernel.org> # 4.17+
Test-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Reviewed-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index ea04dfb8c092..2d8fc8c9da7a 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1314,9 +1314,7 @@ EXC_REAL_BEGIN(denorm_exception_hv, 0x1500, 0x100)
 
 #ifdef CONFIG_PPC_DENORMALISATION
         mfspr   r10,SPRN_HSRR1
-        mfspr   r11,SPRN_HSRR0          /* save HSRR0 */
         andis.  r10,r10,(HSRR1_DENORM)@h /* denorm? */
-        addi    r11,r11,-4              /* HSRR0 is next instruction */
         bne+    denorm_assist
 #endif
 
@@ -1382,6 +1380,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
  */
         XVCPSGNDP32(32)
 denorm_done:
+        mfspr   r11,SPRN_HSRR0
+        subi    r11,r11,4
         mtspr   SPRN_HSRR0,r11
         mtcrf   0x80,r9
         ld      r9,PACA_EXGEN+EX_R9(r13)