On 10/10/2017 10:08 AM, Benjamin Herrenschmidt wrote:
> On Mon, 2017-10-09 at 17:49 +0200, Cédric Le Goater wrote:
>> When a CPU is stopped with the 'stop-self' RTAS call, its state
>> 'halted' is switched to 1 and, in this case, the MSR is not taken into
>> account anymore in the cpu_has_work() routine. Only the pending
>> hardware interrupts are checked with their LPCR:PECE* enablement bit.
>>
>> If the DECR timer fires after 'stop-self' is called and before the CPU
>> 'stop' state is reached, the nearly-dead CPU will have some work to do
>> and the guest will crash. This case happens very frequently with the
>> not yet upstream P9 XIVE exploitation mode. In XICS mode, the DECR is
>> occasionally fired but after 'stop' state, so no work is to be done
>> and the guest survives.
>>
>> I suspect there is a race between the QEMU mainloop triggering the
>> timers and the TCG CPU thread but I could not quite identify the root
>> cause. To be safe, let's disable the decrementer interrupt in the LPCR
>> when the CPU is halted and reenable it when the CPU is restarted.
>>
>> Signed-off-by: Cédric Le Goater <c...@kaod.org>
>
> We should disable external interrupts and doorbells too no ? IE, we
> could clear all of PECE in fact.
and enable them all in 'start-cpu' for secondaries then ?
C.
>
>> ---
>>
>> Changes in v2:
>>
>> - used a new routine ppc_cpu_pvr_match() to discriminate CPU versions
>> - removed the LPCR:PECE* enablement bit when the CPU is initialized
>> if it is a secondary
>>
>> hw/ppc/spapr_rtas.c | 20 ++++++++++++++++++++
>> target/ppc/translate_init.c | 19 +++++++++++++++++--
>> 2 files changed, 37 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>> index cdf0b607a0a0..dfdbf1e2c6f8 100644
>> --- a/hw/ppc/spapr_rtas.c
>> +++ b/hw/ppc/spapr_rtas.c
>> @@ -46,6 +46,7 @@
>> #include "qemu/cutils.h"
>> #include "trace.h"
>> #include "hw/ppc/fdt.h"
>> +#include "target/ppc/cpu-models.h"
>>
>> static void rtas_display_character(PowerPCCPU *cpu, sPAPRMachineState
>> *spapr,
>> uint32_t token, uint32_t nargs,
>> @@ -174,6 +175,15 @@ static void rtas_start_cpu(PowerPCCPU *cpu_,
>> sPAPRMachineState *spapr,
>> kvm_cpu_synchronize_state(cs);
>>
>> env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
>> +
>> + /* Enable DECR interrupt */
>> + if (ppc_cpu_pvr_match(cpu, CPU_POWERPC_LOGICAL_3_00)) {
>> + env->spr[SPR_LPCR] |= LPCR_DEE;
>> + } else {
>> + /* P7 and P8 both have same bit for DECR */
>> + env->spr[SPR_LPCR] |= LPCR_P8_PECE3;
>> + }
>> +
>> env->nip = start;
>> env->gpr[3] = r3;
>> cs->halted = 0;
>> @@ -210,6 +220,16 @@ static void rtas_stop_self(PowerPCCPU *cpu,
>> sPAPRMachineState *spapr,
>> * no need to bother with specific bits, we just clear it.
>> */
>> env->msr = 0;
>> +
>> + /* Don't let the decremeter run on a CPU being stopped. This could
>> + * deliver an interrupt on a dying CPU and crash the guest.
>> + */
>> + if (ppc_cpu_pvr_match(cpu, CPU_POWERPC_LOGICAL_3_00)) {
>> + env->spr[SPR_LPCR] &= ~LPCR_DEE;
>> + } else {
>> + /* P7 and P8 both have same bit for DECR */
>> + env->spr[SPR_LPCR] &= ~LPCR_P8_PECE3;
>> + }
>> }
>>
>> static inline int sysparm_st(target_ulong addr, target_ulong len,
>> diff --git a/target/ppc/translate_init.c b/target/ppc/translate_init.c
>> index 0d6379fcc5b4..1a62159843e7 100644
>> --- a/target/ppc/translate_init.c
>> +++ b/target/ppc/translate_init.c
>> @@ -8905,6 +8905,7 @@ void cpu_ppc_set_papr(PowerPCCPU *cpu,
>> PPCVirtualHypervisor *vhyp)
>> CPUPPCState *env = &cpu->env;
>> ppc_spr_t *lpcr = &env->spr_cb[SPR_LPCR];
>> ppc_spr_t *amor = &env->spr_cb[SPR_AMOR];
>> + CPUState *cs = CPU(cpu);
>>
>> cpu->vhyp = vhyp;
>>
>> @@ -8946,8 +8947,15 @@ void cpu_ppc_set_papr(PowerPCCPU *cpu,
>> PPCVirtualHypervisor *vhyp)
>> } else {
>> lpcr->default_value &= ~(LPCR_UPRT | LPCR_GTSE);
>> }
>> - lpcr->default_value |= LPCR_PDEE | LPCR_HDEE | LPCR_EEE | LPCR_DEE |
>> + lpcr->default_value |= LPCR_PDEE | LPCR_HDEE | LPCR_EEE |
>> LPCR_OEE;
>> +
>> + /* Only let the decremeter wake up the boot CPU. The RTAS
>> + * command start-cpu will enable it on secondaries.
>> + */
>> + if (cs == first_cpu) {
>> + lpcr->default_value |= LPCR_DEE;
>> + }
>> break;
>> default:
>> /* P7 and P8 has slightly different PECE bits, mostly because P8
>> adds
>> @@ -8955,7 +8963,14 @@ void cpu_ppc_set_papr(PowerPCCPU *cpu,
>> PPCVirtualHypervisor *vhyp)
>> * will work as expected for both implementations
>> */
>> lpcr->default_value |= LPCR_P8_PECE0 | LPCR_P8_PECE1 |
>> LPCR_P8_PECE2 |
>> - LPCR_P8_PECE3 | LPCR_P8_PECE4;
>> + LPCR_P8_PECE4;
>> +
>> + /* Only let the decremeter wake up the boot CPU. The RTAS
>> + * command start-cpu will enable it on secondaries.
>> + */
>> + if (cs == first_cpu) {
>> + lpcr->default_value |= LPCR_P8_PECE3;
>> + }
>> }
>>
>> /* We should be followed by a CPU reset but update the active value
