[PATCH] KVM: PPC: Book3S HV: Fix r3 corruption in h_set_dabr()

[Michael Neuling]

In commit c1fe190c0672 ("powerpc: Add force enable of DAWR on P9
option") I screwed up some assembler and corrupted a pointer in
r3. This resulted in crashes like the below from Cédric:

  [   44.374746] BUG: Kernel NULL pointer dereference at 0x000013bf
  [   44.374848] Faulting instruction address: 0xc00000000010b044
  [   44.374906] Oops: Kernel access of bad area, sig: 11 [#1]
  [   44.374951] LE PAGE_SIZE=64K MMU=Radix MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
  [   44.375018] Modules linked in: vhost_net vhost tap xt_CHECKSUM iptable_mangle xt_MASQUERADE iptable_nat nf_nat xt_conntrack nf_conntrack nf_defrag_ipv6 libcrc32c nf_defrag_ipv4 ipt_REJECT nf_reject_ipv4 xt_tcpudp bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter bpfilter vmx_crypto crct10dif_vpmsum crc32c_vpmsum kvm_hv kvm sch_fq_codel ip_tables x_tables autofs4 virtio_net net_failover virtio_scsi failover
  [   44.375401] CPU: 8 PID: 1771 Comm: qemu-system-ppc Kdump: loaded Not tainted 5.2.0-rc4+ #3
  [   44.375500] NIP:  c00000000010b044 LR: c0080000089dacf4 CTR: c00000000010aff4
  [   44.375604] REGS: c00000179b397710 TRAP: 0300   Not tainted  (5.2.0-rc4+)
  [   44.375691] MSR:  800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 42244842  XER: 00000000
  [   44.375815] CFAR: c00000000010aff8 DAR: 00000000000013bf DSISR: 42000000 IRQMASK: 0
  [   44.375815] GPR00: c0080000089dd6bc c00000179b3979a0 c008000008a04300 ffffffffffffffff
  [   44.375815] GPR04: 0000000000000000 0000000000000003 000000002444b05d c0000017f11c45d0
  [   44.375815] GPR08: 078000003e018dfe 0000000000000028 0000000000000001 0000000000000075
  [   44.375815] GPR12: c00000000010aff4 c000000007ff6300 0000000000000000 0000000000000000
  [   44.375815] GPR16: 0000000000000000 c0000017f11d0000 00000000ffffffff c0000017f11ca7a8
  [   44.375815] GPR20: c0000017f11c42ec ffffffffffffffff 0000000000000000 000000000000000a
  [   44.375815] GPR24: fffffffffffffffc 0000000000000000 c0000017f11c0000 c000000001a77ed8
  [   44.375815] GPR28: c00000179af70000 fffffffffffffffc c0080000089ff170 c00000179ae88540
  [   44.376673] NIP [c00000000010b044] kvmppc_h_set_dabr+0x50/0x68
  [   44.376754] LR [c0080000089dacf4] kvmppc_pseries_do_hcall+0xa3c/0xeb0 [kvm_hv]
  [   44.376849] Call Trace:
  [   44.376886] [c00000179b3979a0] [c0000017f11c0000] 0xc0000017f11c0000 (unreliable)
  [   44.376982] [c00000179b397a10] [c0080000089dd6bc] kvmppc_vcpu_run_hv+0x694/0xec0 [kvm_hv]
  [   44.377084] [c00000179b397ae0] [c0080000093f8bcc] kvmppc_vcpu_run+0x34/0x48 [kvm]
  [   44.377185] [c00000179b397b00] [c0080000093f522c] kvm_arch_vcpu_ioctl_run+0x2f4/0x400 [kvm]
  [   44.377286] [c00000179b397b90] [c0080000093e3618] kvm_vcpu_ioctl+0x460/0x850 [kvm]
  [   44.377384] [c00000179b397d00] [c0000000004ba6c4] do_vfs_ioctl+0xe4/0xb40
  [   44.377464] [c00000179b397db0] [c0000000004bb1e4] ksys_ioctl+0xc4/0x110
  [   44.377547] [c00000179b397e00] [c0000000004bb258] sys_ioctl+0x28/0x80
  [   44.377628] [c00000179b397e20] [c00000000000b888] system_call+0x5c/0x70
  [   44.377712] Instruction dump:
  [   44.377765] 4082fff4 4c00012c 38600000 4e800020 e96280c0 896b0000 2c2b0000 3860ffff
  [   44.377862] 4d820020 50852e74 508516f6 78840724 <f88313c0> f8a313c8 7c942ba6 7cbc2ba6

This fixes the problem by only changing r3 when we are returning
immediately.

Signed-off-by: Michael Neuling <mikey at neuling.org>
Reported-by: Cédric Le Goater <clg at kaod.org>
--
mpe: This is for 5.2 fixes
---
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 139027c62d..f781ee1458 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -2519,8 +2519,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	LOAD_REG_ADDR(r11, dawr_force_enable)
 	lbz	r11, 0(r11)
 	cmpdi	r11, 0
+	bne	3f
 	li	r3, H_HARDWARE
-	beqlr
+	blr
+3:
 	/* Emulate H_SET_DABR/X on P8 for the sake of compat mode guests */
 	rlwimi	r5, r4, 5, DAWRX_DR | DAWRX_DW
 	rlwimi	r5, r4, 2, DAWRX_WT
-- 
2.21.0