Re: [PATCH v4 2/3] target/riscv: Add stimecmp support

[Alistair Francis]

On Sat, May 14, 2022 at 4:39 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> stimecmp allows the supervisor mode to update stimecmp CSR directly
> to program the next timer interrupt. This CSR is part of the Sstc
> extension which was ratified recently.
>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  target/riscv/cpu.c         |  8 ++++
>  target/riscv/cpu.h         |  7 +++
>  target/riscv/cpu_bits.h    |  4 ++
>  target/riscv/csr.c         | 92 +++++++++++++++++++++++++++++++++++
>  target/riscv/machine.c     |  2 +
>  target/riscv/meson.build   |  3 +-
>  target/riscv/time_helper.c | 98 ++++++++++++++++++++++++++++++++++++++
>  target/riscv/time_helper.h | 30 ++++++++++++
>  8 files changed, 243 insertions(+), 1 deletion(-)
>  create mode 100644 target/riscv/time_helper.c
>  create mode 100644 target/riscv/time_helper.h
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 19f4e8294042..d58dd2f857a7 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -23,6 +23,7 @@
>  #include "qemu/log.h"
>  #include "cpu.h"
>  #include "internals.h"
> +#include "time_helper.h"
>  #include "exec/exec-all.h"
>  #include "qapi/error.h"
>  #include "qemu/error-report.h"
> @@ -779,7 +780,12 @@ static void riscv_cpu_init(Object *obj)
>  #ifndef CONFIG_USER_ONLY
>      qdev_init_gpio_in(DEVICE(cpu), riscv_cpu_set_irq,
>                        IRQ_LOCAL_MAX + IRQ_LOCAL_GUEST_MAX);
> +
> +    if (cpu->cfg.ext_sstc) {
> +        riscv_timer_init(cpu);
> +    }
>  #endif /* CONFIG_USER_ONLY */
> +
>  }
>
>  static Property riscv_cpu_properties[] = {
> @@ -806,6 +812,7 @@ static Property riscv_cpu_properties[] = {
>      DEFINE_PROP_BOOL("mmu", RISCVCPU, cfg.mmu, true),
>      DEFINE_PROP_BOOL("pmp", RISCVCPU, cfg.pmp, true),
>      DEFINE_PROP_BOOL("debug", RISCVCPU, cfg.debug, true),
> +    DEFINE_PROP_BOOL("sstc", RISCVCPU, cfg.ext_sstc, true),
>
>      DEFINE_PROP_STRING("priv_spec", RISCVCPU, cfg.priv_spec),
>      DEFINE_PROP_STRING("vext_spec", RISCVCPU, cfg.vext_spec),
> @@ -965,6 +972,7 @@ static void riscv_isa_string_ext(RISCVCPU *cpu, char 
> **isa_str, int max_str_len)
>          ISA_EDATA_ENTRY(zbs, ext_zbs),
>          ISA_EDATA_ENTRY(zve32f, ext_zve32f),
>          ISA_EDATA_ENTRY(zve64f, ext_zve64f),
> +        ISA_EDATA_ENTRY(sstc, ext_sstc),
>          ISA_EDATA_ENTRY(svinval, ext_svinval),
>          ISA_EDATA_ENTRY(svnapot, ext_svnapot),
>          ISA_EDATA_ENTRY(svpbmt, ext_svpbmt),
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 1119d5201066..9a01e6d0f587 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -276,6 +276,11 @@ struct CPUArchState {
>      uint64_t mfromhost;
>      uint64_t mtohost;
>
> +    /* Sstc CSRs */
> +    uint64_t stimecmp;
> +    /* For RV32 only */
> +    uint8_t stimecmp_wr_done;
> +
>      /* physical memory protection */
>      pmp_table_t pmp_state;
>      target_ulong mseccfg;
> @@ -329,6 +334,7 @@ struct CPUArchState {
>      float_status fp_status;
>
>      /* Fields from here on are preserved across CPU reset. */
> +    QEMUTimer *stimer; /* Internal timer for S-mode interrupt */
>
>      hwaddr kernel_addr;
>      hwaddr fdt_addr;
> @@ -379,6 +385,7 @@ struct RISCVCPUConfig {
>      bool ext_counters;
>      bool ext_ifencei;
>      bool ext_icsr;
> +    bool ext_sstc;
>      bool ext_svinval;
>      bool ext_svnapot;
>      bool ext_svpbmt;
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index 4e5b630f5965..29d0e4a1be01 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -215,6 +215,10 @@
>  #define CSR_STVAL           0x143
>  #define CSR_SIP             0x144
>
> +/* Sstc supervisor CSRs */
> +#define CSR_STIMECMP        0x14D
> +#define CSR_STIMECMPH       0x15D
> +
>  /* Supervisor Protection and Translation */
>  #define CSR_SPTBR           0x180
>  #define CSR_SATP            0x180
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index 245f007e66e1..8952d1308008 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -21,6 +21,7 @@
>  #include "qemu/log.h"
>  #include "qemu/timer.h"
>  #include "cpu.h"
> +#include "time_helper.h"
>  #include "qemu/main-loop.h"
>  #include "exec/exec-all.h"
>  #include "sysemu/cpu-timers.h"
> @@ -537,6 +538,87 @@ static RISCVException read_timeh(CPURISCVState *env, int 
> csrno,
>      return RISCV_EXCP_NONE;
>  }
>
> +static RISCVException sstc(CPURISCVState *env, int csrno)
> +{
> +    CPUState *cs = env_cpu(env);
> +    RISCVCPU *cpu = RISCV_CPU(cs);
> +
> +    if (!cpu->cfg.ext_sstc || !env->rdtime_fn) {
> +        return RISCV_EXCP_ILLEGAL_INST;
> +    }
> +
> +    if (env->priv == PRV_M) {
> +        return RISCV_EXCP_NONE;
> +    }
> +
> +    if (env->priv != PRV_S) {
> +        return RISCV_EXCP_ILLEGAL_INST;
> +    }
> +
> +    /*
> +     * No need of separate function for rv32 as menvcfg stores both menvcfg
> +     * menvcfgh for RV32.
> +     */
> +    if (!(get_field(env->mcounteren, COUNTEREN_TM) &&
> +          get_field(env->menvcfg, MENVCFG_STCE))) {
> +        return RISCV_EXCP_ILLEGAL_INST;
> +    }
> +
> +    return RISCV_EXCP_NONE;
> +}
> +
> +static RISCVException read_stimecmp(CPURISCVState *env, int csrno,
> +                                    target_ulong *val)
> +{
> +    *val = env->stimecmp;
> +    return RISCV_EXCP_NONE;
> +}
> +
> +static RISCVException read_stimecmph(CPURISCVState *env, int csrno,
> +                                    target_ulong *val)
> +{
> +    *val = env->stimecmp >> 32;
> +    return RISCV_EXCP_NONE;
> +}
> +
> +static RISCVException write_stimecmp(CPURISCVState *env, int csrno,
> +                                    target_ulong val)
> +{
> +    RISCVCPU *cpu = env_archcpu(env);
> +
> +    if (riscv_cpu_mxl(env) == MXL_RV32) {
> +        env->stimecmp = deposit64(env->stimecmp, 0, 32, (uint64_t)val);
> +        env->stimecmp_wr_done |= 0x01;
> +        if (env->stimecmp_wr_done != 0x03) {

This still doesn't seem right. What if a guest already knows the top
32-bits are 0 and just writes the bottom 32-bits? In this case we
won't generate an interrupt, which is incorrect

That's unlikely to happen, but we should aim to model the spec, not
what we think people will do.

We should just be able to call riscv_timer_write_timecmp() on all updates

Alistair

> +            return RISCV_EXCP_NONE;
> +        } else {
> +            env->stimecmp_wr_done = 0;
> +        }
> +    } else {
> +        env->stimecmp = val;
> +    }
> +
> +    riscv_timer_write_timecmp(cpu, env->stimer, env->stimecmp, 0, MIP_STIP);
> +
> +    return RISCV_EXCP_NONE;
> +}
> +
> +static RISCVException write_stimecmph(CPURISCVState *env, int csrno,
> +                                    target_ulong val)
> +{
> +    RISCVCPU *cpu = env_archcpu(env);
> +
> +    env->stimecmp = deposit64(env->stimecmp, 32, 32, (uint64_t)val);
> +    env->stimecmp_wr_done |= 0x02;
> +    if (env->stimecmp_wr_done != 0x03) {
> +        return RISCV_EXCP_NONE;
> +    }
> +    env->stimecmp_wr_done = 0;
> +    riscv_timer_write_timecmp(cpu, env->stimer, env->stimecmp, 0, MIP_STIP);
> +
> +    return RISCV_EXCP_NONE;
> +}
> +
>  /* Machine constants */
>
>  #define M_MODE_INTERRUPTS  ((uint64_t)(MIP_MSIP | MIP_MTIP | MIP_MEIP))
> @@ -1515,6 +1597,12 @@ static RISCVException rmw_mip64(CPURISCVState *env, 
> int csrno,
>          new_val |= env->external_seip * MIP_SEIP;
>      }
>
> +    if (cpu->cfg.ext_sstc && (env->priv == PRV_M) &&
> +        get_field(env->menvcfg, MENVCFG_STCE)) {
> +        /* sstc extension forbids STIP & VSTIP to be writeable in mip */
> +        mask = mask & ~(MIP_STIP | MIP_VSTIP);
> +    }
> +
>      if (mask) {
>          old_mip = riscv_cpu_update_mip(cpu, mask, (new_val & mask));
>      } else {
> @@ -3341,6 +3429,10 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
>      [CSR_SCAUSE]   = { "scause",   smode, read_scause,   write_scause   },
>      [CSR_STVAL]    = { "stval",    smode, read_stval,   write_stval   },
>      [CSR_SIP]      = { "sip",      smode, NULL,    NULL, rmw_sip        },
> +    [CSR_STIMECMP] = { "stimecmp", sstc, read_stimecmp, write_stimecmp,
> +                                          .min_priv_ver = 
> PRIV_VERSION_1_12_0 },
> +    [CSR_STIMECMPH] = { "stimecmph", sstc, read_stimecmph, write_stimecmph,
> +                                          .min_priv_ver = 
> PRIV_VERSION_1_12_0 },
>
>      /* Supervisor Protection and Translation */
>      [CSR_SATP]     = { "satp",     smode, read_satp,    write_satp      },
> diff --git a/target/riscv/machine.c b/target/riscv/machine.c
> index 7d85de0b1d49..1e775343a37b 100644
> --- a/target/riscv/machine.c
> +++ b/target/riscv/machine.c
> @@ -334,6 +334,8 @@ const VMStateDescription vmstate_riscv_cpu = {
>          VMSTATE_UINTTL(env.mscratch, RISCVCPU),
>          VMSTATE_UINT64(env.mfromhost, RISCVCPU),
>          VMSTATE_UINT64(env.mtohost, RISCVCPU),
> +        VMSTATE_UINT64(env.stimecmp, RISCVCPU),
> +        VMSTATE_UINT8(env.stimecmp_wr_done, RISCVCPU),
>
>          VMSTATE_END_OF_LIST()
>      },
> diff --git a/target/riscv/meson.build b/target/riscv/meson.build
> index 2c20f3dd8e9c..1243d019148e 100644
> --- a/target/riscv/meson.build
> +++ b/target/riscv/meson.build
> @@ -29,7 +29,8 @@ riscv_softmmu_ss.add(files(
>    'pmp.c',
>    'debug.c',
>    'monitor.c',
> -  'machine.c'
> +  'machine.c',
> +  'time_helper.c'
>  ))
>
>  target_arch += {'riscv': riscv_ss}
> diff --git a/target/riscv/time_helper.c b/target/riscv/time_helper.c
> new file mode 100644
> index 000000000000..f3fb5eac7b7b
> --- /dev/null
> +++ b/target/riscv/time_helper.c
> @@ -0,0 +1,98 @@
> +/*
> + * RISC-V timer helper implementation.
> + *
> + * Copyright (c) 2022 Rivos Inc.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2 or later, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along 
> with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/log.h"
> +#include "cpu_bits.h"
> +#include "time_helper.h"
> +#include "hw/intc/riscv_aclint.h"
> +
> +static void riscv_stimer_cb(void *opaque)
> +{
> +    RISCVCPU *cpu = opaque;
> +    riscv_cpu_update_mip(cpu, MIP_STIP, BOOL_TO_MASK(1));
> +}
> +
> +/*
> + * Called when timecmp is written to update the QEMU timer or immediately
> + * trigger timer interrupt if mtimecmp <= current timer value.
> + */
> +void riscv_timer_write_timecmp(RISCVCPU *cpu, QEMUTimer *timer,
> +                               uint64_t timecmp, uint64_t delta,
> +                               uint32_t timer_irq)
> +{
> +    uint64_t diff, ns_diff, next;
> +    CPURISCVState *env = &cpu->env;
> +    RISCVAclintMTimerState *mtimer = env->rdtime_fn_arg;
> +    uint32_t timebase_freq = mtimer->timebase_freq;
> +    uint64_t rtc_r = env->rdtime_fn(env->rdtime_fn_arg) + delta;
> +
> +    if (timecmp <= rtc_r) {
> +        /*
> +         * If we're setting an stimecmp value in the "past",
> +         * immediately raise the timer interrupt
> +         */
> +        riscv_cpu_update_mip(cpu, timer_irq, BOOL_TO_MASK(1));
> +        return;
> +    }
> +
> +    /* Clear the [V]STIP bit in mip */
> +    riscv_cpu_update_mip(cpu, timer_irq, BOOL_TO_MASK(0));
> +
> +    /* otherwise, set up the future timer interrupt */
> +    diff = timecmp - rtc_r;
> +    /* back to ns (note args switched in muldiv64) */
> +    ns_diff = muldiv64(diff, NANOSECONDS_PER_SECOND, timebase_freq);
> +
> +    /*
> +     * check if ns_diff overflowed and check if the addition would 
> potentially
> +     * overflow
> +     */
> +    if ((NANOSECONDS_PER_SECOND > timebase_freq && ns_diff < diff) ||
> +        ns_diff > INT64_MAX) {
> +        next = INT64_MAX;
> +    } else {
> +        /*
> +         * as it is very unlikely qemu_clock_get_ns will return a value
> +         * greater than INT64_MAX, no additional check is needed for an
> +         * unsigned integer overflow.
> +         */
> +        next = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + ns_diff;
> +        /*
> +         * if ns_diff is INT64_MAX next may still be outside the range
> +         * of a signed integer.
> +         */
> +        next = MIN(next, INT64_MAX);
> +    }
> +
> +    timer_mod(timer, next);
> +}
> +
> +void riscv_timer_init(RISCVCPU *cpu)
> +{
> +    CPURISCVState *env;
> +
> +    if (!cpu) {
> +        return;
> +    }
> +
> +    env = &cpu->env;
> +    env->stimer = timer_new_ns(QEMU_CLOCK_VIRTUAL, &riscv_stimer_cb, cpu);
> +    env->stimecmp = 0;
> +
> +}
> diff --git a/target/riscv/time_helper.h b/target/riscv/time_helper.h
> new file mode 100644
> index 000000000000..7b3cdcc35020
> --- /dev/null
> +++ b/target/riscv/time_helper.h
> @@ -0,0 +1,30 @@
> +/*
> + * RISC-V timer header file.
> + *
> + * Copyright (c) 2022 Rivos Inc.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2 or later, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along 
> with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef RISCV_TIME_HELPER_H
> +#define RISCV_TIME_HELPER_H
> +
> +#include "cpu.h"
> +#include "qemu/timer.h"
> +
> +void riscv_timer_write_timecmp(RISCVCPU *cpu, QEMUTimer *timer,
> +                               uint64_t timecmp, uint64_t delta,
> +                               uint32_t timer_irq);
> +void riscv_timer_init(RISCVCPU *cpu);
> +
> +#endif
> --
> 2.25.1
>
>