Daniel Henrique Barboza <danielhb...@gmail.com> writes:
> This patch adds the EBB exception support that are triggered by
> Performance Monitor alerts. This happens when a Performance Monitor
> alert occurs and MMCR0_EBE, BESCR_PME and BESCR_GE are set.
>
> A 'ebb_excp_enabled' helper is called at the end of fire_PMC_interrupt()
> to fire the EBB exception, checking for FSCR and HFSCR support
> beforehand.
>
> In ppc_hw_interrupt() the generated EBB exception will be taken only if
> running in problem state and with BESCR_GE set. The check for BESCR_GE
> bit in this step is needed to avoid race conditions where we take an
> EBB, while the previous EBB is still inflight (BESCR_GE cleared), and
> SPR_EBBHR is not set yet. In this case we'll branch to env->nip = 0 and the
> guest will crash. The Linux kernel selftest 'lost_exception_test' is an
> example where this racing will occur.
>
> The code in powerpc_excp_books() is the default EBB handling described
> in the PowerISA v3.1: clear BESCR_GE, set BESCR_PMEO, save env->nip in
> SPR_EBBRR and redirect the execution to the address pointed by
> SPR_EBBHR. The already implemented 'rbebb' instruction is then able to
> return from the EBB by retrieving the NIP in SPR_EBBRR.
>
> Signed-off-by: Daniel Henrique Barboza <danielhb...@gmail.com>
Now that BookS code is separate from the other CPUs, let me leave this
here:
Why do we have "interrupts" before "exceptions"? As in ppc_hw_interrupt
calling powerpc_excp.
If anyone has a consistent mental model on how this that they could
share I'd appreciate it.
Now onto the patch:
> ---
> target/ppc/excp_helper.c | 51 +++++++++++++++++++++++++++++++++++++---
> target/ppc/helper.h | 1 +
> target/ppc/power8-pmu.c | 12 ++++++++--
> 3 files changed, 59 insertions(+), 5 deletions(-)
>
> diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
> index 8a49a4ab90..2a95cec39e 100644
> --- a/target/ppc/excp_helper.c
> +++ b/target/ppc/excp_helper.c
> @@ -19,6 +19,7 @@
> #include "qemu/osdep.h"
> #include "qemu/main-loop.h"
> #include "cpu.h"
> +#include "hw/ppc/ppc.h"
> #include "exec/exec-all.h"
> #include "internal.h"
> #include "helper_regs.h"
> @@ -990,8 +991,22 @@ static void powerpc_excp_books(PowerPCCPU *cpu, int excp)
> new_msr |= (target_ulong)MSR_HVB;
> new_msr |= env->msr & ((target_ulong)1 << MSR_RI);
> break;
> - case POWERPC_EXCP_THERM: /* Thermal interrupt
> */
> case POWERPC_EXCP_PERFM: /* Embedded performance monitor interrupt
> */
We would need some way to tell apart EBB from other Performance Monitor
interrupts here. Unless you want to leave that to the next person that
looks at Performance Monitor interrupts.
> + env->spr[SPR_BESCR] &= ~BESCR_GE;
> + env->spr[SPR_BESCR] |= BESCR_PMEO;
> +
> + /*
> + * Save NIP for rfebb insn in SPR_EBBRR. Next nip is
> + * stored in the EBB Handler SPR_EBBHR.
> + */
> + env->spr[SPR_EBBRR] = env->nip;
> + powerpc_set_excp_state(cpu, env->spr[SPR_EBBHR], env->msr);
> +
> + /*
> + * This exception is handled in userspace. No need to proceed.
> + */
> + return;
> + case POWERPC_EXCP_THERM: /* Thermal interrupt
> */
> case POWERPC_EXCP_VPUA: /* Vector assist exception
> */
> case POWERPC_EXCP_MAINT: /* Maintenance exception
> */
> case POWERPC_EXCP_SDOOR: /* Doorbell interrupt
> */
> @@ -1671,8 +1686,14 @@ static void ppc_hw_interrupt(CPUPPCState *env)
> return;
> }
> if (env->pending_interrupts & (1 << PPC_INTERRUPT_PERFM)) {
> - env->pending_interrupts &= ~(1 << PPC_INTERRUPT_PERFM);
> - powerpc_excp(cpu, POWERPC_EXCP_PERFM);
> + /*
> + * PERFM EBB must be taken in problem state and
> + * with BESCR_GE set.
> + */
> + if (msr_pr == 1 && env->spr[SPR_BESCR] & BESCR_GE) {
> + env->pending_interrupts &= ~(1 << PPC_INTERRUPT_PERFM);
> + powerpc_excp(cpu, POWERPC_EXCP_PERFM);
> + }
This is masking other Performance Interrupts (for all CPUs). Can we move
these checks into the helper?
> return;
> }
> /* Thermal interrupt */
> @@ -1915,6 +1936,30 @@ void helper_rfebb(CPUPPCState *env, target_ulong s)
> env->spr[SPR_BESCR] &= ~BESCR_GE;
> }
> }
> +
> +void helper_ebb_perfm_int(CPUPPCState *env)
> +{
> + PowerPCCPU *cpu = env_archcpu(env);
> +
> + /*
> + * FSCR_EBB and FSCR_IC_EBB are the same bits used with
> + * HFSCR.
> + */
> + helper_fscr_facility_check(env, FSCR_EBB, 0, FSCR_IC_EBB);
> + helper_hfscr_facility_check(env, FSCR_EBB, "EBB", FSCR_IC_EBB);
> +
> + /*
> + * Setting "env->pending_interrupts |= 1 << PPC_INTERRUPT_PERFM"
> + * instead of calling "ppc_set_irq()"" works in most cases, but under
> + * certain race conditions (e.g. lost_exception_test EBB kernel
> + * selftest) this hits an assert when dealing with the BQL:
> + *
> + * tcg_handle_interrupt: assertion failed: (qemu_mutex_iothread_locked())
> + *
> + * We ended up using ppc_set_irq() because it handles the BQL.
> + */
> + ppc_set_irq(cpu, PPC_INTERRUPT_PERFM, 1);
> +}
> #endif
>
>
> /*****************************************************************************/
> diff --git a/target/ppc/helper.h b/target/ppc/helper.h
> index f2e5060910..bb26da6176 100644
> --- a/target/ppc/helper.h
> +++ b/target/ppc/helper.h
> @@ -19,6 +19,7 @@ DEF_HELPER_1(rfid, void, env)
> DEF_HELPER_1(rfscv, void, env)
> DEF_HELPER_1(hrfid, void, env)
> DEF_HELPER_2(rfebb, void, env, tl)
> +DEF_HELPER_1(ebb_perfm_int, void, env)
> DEF_HELPER_2(store_lpcr, void, env, tl)
> DEF_HELPER_2(store_pcr, void, env, tl)
> DEF_HELPER_2(store_mmcr0, void, env, tl)
> diff --git a/target/ppc/power8-pmu.c b/target/ppc/power8-pmu.c
> index d245663158..41409e609f 100644
> --- a/target/ppc/power8-pmu.c
> +++ b/target/ppc/power8-pmu.c
> @@ -281,6 +281,13 @@ void helper_store_pmc(CPUPPCState *env, uint32_t sprn,
> uint64_t value)
> pmc_update_overflow_timer(env, sprn);
> }
>
> +static bool ebb_excp_enabled(CPUPPCState *env)
> +{
> + return env->spr[SPR_POWER_MMCR0] & MMCR0_EBE &&
> + env->spr[SPR_BESCR] & BESCR_PME &&
> + env->spr[SPR_BESCR] & BESCR_GE;
> +}
> +
> static void fire_PMC_interrupt(PowerPCCPU *cpu)
> {
> CPUPPCState *env = &cpu->env;
> @@ -307,8 +314,9 @@ static void fire_PMC_interrupt(PowerPCCPU *cpu)
> env->spr[SPR_POWER_MMCR0] |= MMCR0_PMAO;
> }
>
> - /* PMC interrupt not implemented yet */
> - return;
> + if (ebb_excp_enabled(env)) {
> + helper_ebb_perfm_int(env);
> + }
> }
>
> /* This helper assumes that the PMC is running. */
