While running a nested guest VCPU on L0 via H_ENTER_NESTED hcall, a
pending signal in the L0 QEMU process can generate the following
sequence:
ret0 = kvmppc_pseries_do_hcall()
ret1 = kvmhv_enter_nested_guest()
ret2 = kvmhv_run_single_vcpu()
if (ret2 == -EINTR)
return H_INTERRUPT
if (ret1 == H_INTERRUPT)
kvmppc_set_gpr(vcpu, 3, 0)
return -EINTR
/* skipped: */
kvmppc_set_gpr(vcpu, 3, ret)
vcpu->arch.hcall_needed = 0
return RESUME_GUEST
which causes an exit to L0 userspace with ret0 == -EINTR.
The intention seems to be to set the hcall return value to 0 (via
VCPU r3) so that L1 will see a successful return from H_ENTER_NESTED
once we resume executing the VCPU. However, because we don't set
vcpu->arch.hcall_needed = 0, we do the following once userspace
resumes execution via kvm_arch_vcpu_ioctl_run():
...
} else if (vcpu->arch.hcall_needed) {
int i
kvmppc_set_gpr(vcpu, 3, run->papr_hcall.ret);
for (i = 0; i < 9; ++i)
kvmppc_set_gpr(vcpu, 4 + i, run->papr_hcall.args[i]);
vcpu->arch.hcall_needed = 0;
since vcpu->arch.hcall_needed == 1 indicates that userspace should
have handled the hcall and stored the return value in
run->papr_hcall.ret. Since that's not the case here, we can get an
unexpected value in VCPU r3, which can result in
kvmhv_p9_guest_entry() reporting an unexpected trap value when it
returns from H_ENTER_NESTED, causing the following register dump to
console via subsequent call to kvmppc_handle_exit_hv() in L1:
[ 350.612854] vcpu 00000000f9564cf8 (0):
[ 350.612915] pc = c00000000013eb98 msr = 8000000000009033 trap = 1
[ 350.613020] r 0 = c0000000004b9044 r16 = 0000000000000000
[ 350.613075] r 1 = c00000007cffba30 r17 = 0000000000000000
[ 350.613120] r 2 = c00000000178c100 r18 = 00007fffc24f3b50
[ 350.613166] r 3 = c00000007ef52480 r19 = 00007fffc24fff58
[ 350.613212] r 4 = 0000000000000000 r20 = 00000a1e96ece9d0
[ 350.613253] r 5 = 70616d00746f6f72 r21 = 00000a1ea117c9b0
[ 350.613295] r 6 = 0000000000000020 r22 = 00000a1ea1184360
[ 350.613338] r 7 = c0000000783be440 r23 = 0000000000000003
[ 350.613380] r 8 = fffffffffffffffc r24 = 00000a1e96e9e124
[ 350.613423] r 9 = c00000007ef52490 r25 = 00000000000007ff
[ 350.613469] r10 = 0000000000000004 r26 = c00000007eb2f7a0
[ 350.613513] r11 = b0616d0009eccdb2 r27 = c00000007cffbb10
[ 350.613556] r12 = c0000000004b9000 r28 = c00000007d83a2c0
[ 350.613597] r13 = c000000001b00000 r29 = c0000000783cdf68
[ 350.613639] r14 = 0000000000000000 r30 = 0000000000000000
[ 350.613681] r15 = 0000000000000000 r31 = c00000007cffbbf0
[ 350.613723] ctr = c0000000004b9000 lr = c0000000004b9044
[ 350.613765] srr0 = 0000772f954dd48c srr1 = 800000000280f033
[ 350.613808] sprg0 = 0000000000000000 sprg1 = c000000001b00000
[ 350.613859] sprg2 = 0000772f9565a280 sprg3 = 0000000000000000
[ 350.613911] cr = 88002848 xer = 0000000020040000 dsisr = 42000000
[ 350.613962] dar = 0000772f95390000
[ 350.614031] fault dar = c000000244b278c0 dsisr = 00000000
[ 350.614073] SLB (0 entries):
[ 350.614157] lpcr = 0040000003d40413 sdr1 = 0000000000000000 last_inst = ffffffff
[ 350.614252] trap=0x1 | pc=0xc00000000013eb98 | msr=0x8000000000009033
followed by L1's QEMU reporting the following before stopping execution
of the nested guest:
KVM: unknown exit, hardware reason 1
NIP c00000000013eb98 LR c0000000004b9044 CTR c0000000004b9000 XER 0000000020040000 CPU#0
MSR 8000000000009033 HID0 0000000000000000 HF 8000000000000000 iidx 3 didx 3
TB 00000000 00000000 DECR 00000000
GPR00 c0000000004b9044 c00000007cffba30 c00000000178c100 c00000007ef52480
GPR04 0000000000000000 70616d00746f6f72 0000000000000020 c0000000783be440
GPR08 fffffffffffffffc c00000007ef52490 0000000000000004 b0616d0009eccdb2
GPR12 c0000000004b9000 c000000001b00000 0000000000000000 0000000000000000
GPR16 0000000000000000 0000000000000000 00007fffc24f3b50 00007fffc24fff58
GPR20 00000a1e96ece9d0 00000a1ea117c9b0 00000a1ea1184360 0000000000000003
GPR24 00000a1e96e9e124 00000000000007ff c00000007eb2f7a0 c00000007cffbb10
GPR28 c00000007d83a2c0 c0000000783cdf68 0000000000000000 c00000007cffbbf0
CR 88002848 [ L L - - E L G L ] RES ffffffffffffffff
SRR0 0000772f954dd48c SRR1 800000000280f033 PVR 00000000004e1202 VRSAVE 0000000000000000
SPRG0 0000000000000000 SPRG1 c000000001b00000 SPRG2 0000772f9565a280 SPRG3 0000000000000000
SPRG4 0000000000000000 SPRG5 0000000000000000 SPRG6 0000000000000000 SPRG7 0000000000000000
HSRR0 0000000000000000 HSRR1 0000000000000000
CFAR 0000000000000000
LPCR 0000000003d40413
PTCR 0000000000000000 DAR 0000772f95390000 DSISR 0000000042000000
Fix this by setting vcpu->arch.hcall_needed = 0 to indicate completion
of H_ENTER_NESTED before we exit to L0 userspace.
Cc: linuxppc-dev@xxxxxxxxxx
Cc: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Cc: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index d65b961661fb..a56f8413758a 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -983,6 +983,7 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
ret = kvmhv_enter_nested_guest(vcpu);
if (ret == H_INTERRUPT) {
kvmppc_set_gpr(vcpu, 3, 0);
+ vcpu->arch.hcall_needed = 0;
return -EINTR;
}
break;
--
2.17.1
