Re: [PATCH v3 6/8] hw/intc: GICv3 redistributor ITS processing

[Peter Maydell]

On Fri, 30 Apr 2021 at 00:42, Shashi Mallela <shashi.mallela@linaro.org> wrote:
>
> Implemented lpi processing at redistributor to get lpi config info
> from lpi configuration table,determine priority,set pending state in
> lpi pending table and forward the lpi to cpuif.Added logic to invoke
> redistributor lpi processing with translated LPI which set/clear LPI
> from ITS device as part of ITS INT,CLEAR,DISCARD command and
> GITS_TRANSLATER processing.
>
> Signed-off-by: Shashi Mallela <shashi.mallela@linaro.org>
> ---
>  hw/intc/arm_gicv3.c        |   6 ++
>  hw/intc/arm_gicv3_cpuif.c  |  20 ++++--
>  hw/intc/arm_gicv3_its.c    |  12 ++--
>  hw/intc/arm_gicv3_redist.c | 133 +++++++++++++++++++++++++++++++++++++
>  hw/intc/gicv3_internal.h   |   9 +++
>  5 files changed, 171 insertions(+), 9 deletions(-)
>
> diff --git a/hw/intc/arm_gicv3.c b/hw/intc/arm_gicv3.c
> index 66eaa97198..618fa1af95 100644
> --- a/hw/intc/arm_gicv3.c
> +++ b/hw/intc/arm_gicv3.c
> @@ -166,6 +166,12 @@ static void gicv3_redist_update_noirqset(GICv3CPUState 
> *cs)
>          cs->hppi.grp = gicv3_irq_group(cs->gic, cs, cs->hppi.irq);
>      }
>
> +    if (cs->gic->lpi_enable) {
> +        if (gicv3_redist_update_lpi(cs)) {
> +            seenbetter = true;
> +        }
> +    }
> +

I'm not sure if this call is in the right place. This function
(gicv3_redist_update_noirqset()) is specifically for when state
in the *redistributor* has changed, and it is trying to be a fast
path for "we know that only the redistributor state has changed,
so we might be able to find the new best interrupt by looking only
at the redistributor state". It has a fallback case at the bottom
of the function for "the redistributor state changed such that
we have to actually look at the whole of the GIC state to find
the new best interrupt".

>      /* If the best interrupt we just found would preempt whatever
>       * was the previous best interrupt before this update, then
>       * we know it's definitely the best one now.
> diff --git a/hw/intc/arm_gicv3_cpuif.c b/hw/intc/arm_gicv3_cpuif.c
> index 43ef1d7a84..11b1df5b6b 100644
> --- a/hw/intc/arm_gicv3_cpuif.c
> +++ b/hw/intc/arm_gicv3_cpuif.c
> @@ -899,9 +899,14 @@ static void icc_activate_irq(GICv3CPUState *cs, int irq)
>          cs->gicr_ipendr0 = deposit32(cs->gicr_ipendr0, irq, 1, 0);
>          gicv3_redist_update(cs);
>      } else {
> -        gicv3_gicd_active_set(cs->gic, irq);
> -        gicv3_gicd_pending_clear(cs->gic, irq);
> -        gicv3_update(cs->gic, irq, 1);
> +        if (irq >= GICV3_LPI_INTID_START) {
> +            gicv3_redist_lpi_pending(cs, irq, 0);
> +            gicv3_redist_update(cs);
> +        } else {
> +            gicv3_gicd_active_set(cs->gic, irq);
> +            gicv3_gicd_pending_clear(cs->gic, irq);
> +            gicv3_update(cs->gic, irq, 1);
> +        }

Don't nest this if(), instead write the whole ladder at the same
nesting depth:
    if (irq < GIC_INTERNAL) {
        handle internal irq;
    } else if (irq < GICV3_LPI_INTID_START) {
        handle normal irq;
    } else {
        handle LPI;
    }

>      }
>  }
>
> @@ -1328,7 +1333,8 @@ static void icc_eoir_write(CPUARMState *env, const 
> ARMCPRegInfo *ri,
>          }
>      }
>
> -    if (irq >= cs->gic->num_irq) {
> +    if ((irq >= cs->gic->num_irq) && (!(cs->gic->lpi_enable &&
> +        (irq >= GICV3_LPI_INTID_START)))) {
>          /* This handles two cases:
>           * 1. If software writes the ID of a spurious interrupt [ie 
> 1020-1023]
>           * to the GICC_EOIR, the GIC ignores that write.
> @@ -1348,7 +1354,11 @@ static void icc_eoir_write(CPUARMState *env, const 
> ARMCPRegInfo *ri,
>
>      if (!icc_eoi_split(env, cs)) {
>          /* Priority drop and deactivate not split: deactivate irq now */
> -        icc_deactivate_irq(cs, irq);
> +        if (irq >= GICV3_LPI_INTID_START) {
> +            gicv3_update(cs->gic, irq, 1);

This doesn't look right. You're not actually doing anything here for
an LPI interrupt, so you shouldn't need to call gicv3_update().

> +        } else {
> +            icc_deactivate_irq(cs, irq);
> +        }
>      }
>  }
>
> diff --git a/hw/intc/arm_gicv3_its.c b/hw/intc/arm_gicv3_its.c
> index 98c984dd22..28da2d1d77 100644
> --- a/hw/intc/arm_gicv3_its.c
> +++ b/hw/intc/arm_gicv3_its.c
> @@ -219,6 +219,7 @@ static MemTxResult process_int(GICv3ITSState *s, uint64_t 
> value,
>      bool ite_valid = false;
>      uint64_t cte = 0;
>      bool cte_valid = false;
> +    uint64_t rdbase;
>      uint64_t itel = 0;
>      uint32_t iteh = 0;
>
> @@ -275,10 +276,13 @@ static MemTxResult process_int(GICv3ITSState *s, 
> uint64_t value,
>           * command in the queue
>           */
>      } else {
> -        /*
> -         * Current implementation only supports rdbase == procnum
> -         * Hence rdbase physical address is ignored
> -         */
> +        rdbase = (cte >> 1U) & RDBASE_PROCNUM_MASK;
> +        if ((cmd == CLEAR) || (cmd == DISCARD)) {
> +            gicv3_redist_process_lpi(&s->gicv3->cpu[rdbase], pIntid, 0);
> +        } else {
> +            gicv3_redist_process_lpi(&s->gicv3->cpu[rdbase], pIntid, 1);
> +        }

You need to check that rdbase is actually within the range of the
number of CPUs here, otherwise you might access the cpu[] array
out of bounds.

> +
>          if (cmd == DISCARD) {
>              /* remove mapping from interrupt translation table */
>              res = update_ite(s, eventid, dte, itel, iteh);
> diff --git a/hw/intc/arm_gicv3_redist.c b/hw/intc/arm_gicv3_redist.c
> index 7604ccdc83..82ca9d71e5 100644
> --- a/hw/intc/arm_gicv3_redist.c
> +++ b/hw/intc/arm_gicv3_redist.c
> @@ -256,6 +256,8 @@ static MemTxResult gicr_writel(GICv3CPUState *cs, hwaddr 
> offset,
>          if (cs->gicr_typer & GICR_TYPER_PLPIS) {
>              if (value & GICR_CTLR_ENABLE_LPIS) {
>                  cs->gicr_ctlr |= GICR_CTLR_ENABLE_LPIS;
> +                /* Check for any pending interr in pending table */
> +                gicv3_redist_update(cs);
>              } else {
>                  cs->gicr_ctlr &= ~GICR_CTLR_ENABLE_LPIS;
>              }
> @@ -546,6 +548,137 @@ MemTxResult gicv3_redist_write(void *opaque, hwaddr 
> offset, uint64_t data,
>      return r;
>  }
>
> +bool gicv3_redist_update_lpi(GICv3CPUState *cs)
> +{
> +    /*
> +     * This function scans the LPI pending table and for each pending
> +     * LPI, reads the corresponding entry from LPI configuration table
> +     * to extract the priority info and determine if the LPI priority
> +     * is lower than the current high priority interrupt.If yes, update
> +     * high priority pending interrupt to that of LPI.
> +     */

I would still like to see some profiling of whether we spend a significant
amount of time in this function...

> +    AddressSpace *as = &cs->gic->dma_as;
> +    uint64_t lpict_baddr, lpipt_baddr;
> +    uint32_t pendt_size = 0;
> +    uint8_t lpite;
> +    uint8_t prio, pend;
> +    int i;
> +    bool seenbetter = false;
> +
> +    if ((!cs->gicr_ctlr & GICR_CTLR_ENABLE_LPIS) || !cs->gicr_propbaser ||
> +        !cs->gicr_pendbaser || (FIELD_EX64(cs->gicr_propbaser, 
> GICR_PROPBASER,
> +        IDBITS) < GICR_PROPBASER_IDBITS_THRESHOLD)) {
> +        return seenbetter;
> +    }
> +
> +    lpict_baddr = FIELD_EX64(cs->gicr_propbaser, GICR_PROPBASER, PHYADDR);
> +    lpict_baddr <<= R_GICR_PROPBASER_PHYADDR_SHIFT;
> +
> +    lpipt_baddr =  FIELD_EX64(cs->gicr_pendbaser, GICR_PENDBASER, PHYADDR);
> +    lpipt_baddr <<= R_GICR_PENDBASER_PHYADDR_SHIFT;
> +
> +    /* Determine the highest priority pending interrupt among LPIs */
> +    pendt_size = (1UL << (FIELD_EX64(cs->gicr_propbaser, GICR_PROPBASER,
> +                          IDBITS) - 1));
> +
> +    for (i = 0; i < pendt_size; i++) {
> +        address_space_read(as, lpipt_baddr +
> +                (((GICV3_LPI_INTID_START + i) / 8) * sizeof(pend)),
> +                MEMTXATTRS_UNSPECIFIED, &pend, sizeof(pend));
> +
> +        if ((1 << ((GICV3_LPI_INTID_START + i) % 8)) & pend) {
> +            address_space_read(as, lpict_baddr + (i * sizeof(lpite)),
> +                      MEMTXATTRS_UNSPECIFIED, &lpite, sizeof(lpite));
> +
> +            prio = ((lpite >> LPI_CTE_PRIORITY_OFFSET) &
> +                     LPI_CTE_PRIORITY_MASK);
> +            prio &= LPI_PRIORITY_MASK;


The priority field interpretation depends on whether GICD_CTLR.DS is 0 or 1,
(see section 5.1.1 in the GICv3 spec).

> +
> +            if (prio < cs->hppi.prio) {
> +                cs->hppi.irq = GICV3_LPI_INTID_START + i;
> +                cs->hppi.prio = prio;
> +                /* LPIs are always non-secure Grp1 interrupts */
> +                cs->hppi.grp = GICV3_G1NS;
> +                seenbetter = true;
> +            }
> +        }
> +    }
> +    return seenbetter;
> +}
> +
> +void gicv3_redist_lpi_pending(GICv3CPUState *cs, int irq, int level)
> +{
> +    AddressSpace *as = &cs->gic->dma_as;
> +    uint64_t lpipt_baddr;
> +    bool ispend = false;
> +    uint8_t pend;
> +
> +    /*
> +     * get the bit value corresponding to this irq in the
> +     * lpi pending table
> +     */
> +    lpipt_baddr = FIELD_EX64(cs->gicr_pendbaser, GICR_PENDBASER, PHYADDR);
> +    lpipt_baddr <<= R_GICR_PENDBASER_PHYADDR_SHIFT;

You can write
  lpipt_baddr = cs->gicr_pendbaser & R_GICR_PENDBASER_PHYADDR_MASK;

because the register is laid out deliberately so that bits [51:16] in the
register specify bits [51:16] of the address.

> +
> +    address_space_read(as, lpipt_baddr + ((irq / 8) * sizeof(pend)),
> +                         MEMTXATTRS_UNSPECIFIED, &pend, sizeof(pend));
> +    ispend = ((pend >> (irq % 8)) & 0x1);
> +
> +    if (ispend) {
> +        if (!level) {
> +            /*
> +             * clear the pending bit and update the lpi pending table
> +             */
> +            pend &= ~(1 << (irq % 8));
> +
> +            address_space_write(as, lpipt_baddr + ((irq / 8) * sizeof(pend)),
> +                                 MEMTXATTRS_UNSPECIFIED, &pend, 
> sizeof(pend));
> +        }
> +    } else {
> +        if (level) {
> +            /*
> +             * if pending bit is not already set for this irq,turn-on the
> +             * pending bit and update the lpi pending table
> +             */
> +            pend |= (1 << (irq % 8));
> +
> +            address_space_write(as, lpipt_baddr + ((irq / 8) * sizeof(pend)),
> +                                 MEMTXATTRS_UNSPECIFIED, &pend, 
> sizeof(pend));
> +        }
> +    }
> +}
> +
> +void gicv3_redist_process_lpi(GICv3CPUState *cs, int irq, int level)
> +{
> +    AddressSpace *as = &cs->gic->dma_as;
> +    uint64_t lpict_baddr;
> +    uint8_t lpite;
> +
> +    if ((!cs->gicr_ctlr & GICR_CTLR_ENABLE_LPIS) || !cs->gicr_propbaser ||
> +         !cs->gicr_pendbaser || (FIELD_EX64(cs->gicr_propbaser, 
> GICR_PROPBASER,
> +         IDBITS) < GICR_PROPBASER_IDBITS_THRESHOLD)) {
> +        return;
> +    }

Something needs to be checking for "attempt to work with an interrupt
number that is too large according to either GICR_PROPBASER.IDbits or
GICD_TYPER.IDbits". You could do it either in this function or in the
callers; doing it here is probably as good as anywhere.

> +    lpict_baddr = FIELD_EX64(cs->gicr_propbaser, GICR_PROPBASER, PHYADDR);
> +    lpict_baddr <<= R_GICR_PROPBASER_PHYADDR_SHIFT;
> +
> +    /* get the lpi config table entry corresponding to this irq */
> +    address_space_read(as, lpict_baddr + ((irq - GICV3_LPI_INTID_START) *
> +                        sizeof(lpite)), MEMTXATTRS_UNSPECIFIED,
> +                        &lpite, sizeof(lpite));
> +
> +    /* check if this irq is enabled before proceeding further */
> +    if (!(lpite & LPI_CTE_ENABLED)) {
> +        return;
> +    }
> +
> +    /* set/clear the pending bit for this irq */
> +    gicv3_redist_lpi_pending(cs, irq, level);
> +
> +    gicv3_redist_update(cs);
> +}
> +
>  void gicv3_redist_set_irq(GICv3CPUState *cs, int irq, int level)
>  {
>      /* Update redistributor state for a change in an external PPI input line 
> */

thanks
-- PMM