Re: [Qemu-devel] [RFC 10/17] pseries: Rewrite CAS PVR compatibility logic

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting David Gibson (2016-10-30 06:12:01)
> During boot, PAPR guests negotiate CPU model support with the
> ibm,client-architecture-support mechanism.  The logic to implement this in
> qemu is very convoluted.  This cleans it up to be cleaner, using the new
> ppc_check_compat() call.
> 
> The new logic for choosing a compatibility mode is:
>     1. If the guest lists the CPU's real PVR as supported *AND* no
>        maximum compatibility mode has been requested on the command line
>        then we use "raw" mode - the CPU acts with full capabilities.
>     2. Otherwise, we pick the most recent compatibility mode which is
>        both supported by the CPU, and is advertised as supported by the
>        guest.
> I think the original code approximated the same thing, but it's hard to be
> sure, and I think it had some weird edge cases.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  hw/ppc/spapr_hcall.c | 107 +++++++++++++++++----------------------------------
>  hw/ppc/trace-events  |   2 +-
>  2 files changed, 37 insertions(+), 72 deletions(-)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index d93f580..3bd6d06 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -895,98 +895,63 @@ static void do_set_compat(CPUState *cs, void *arg)
>      ppc_set_compat(cpu, s->compat_pvr, &s->err);
>  }
> 
> -#define get_compat_level(cpuver) ( \
> -    ((cpuver) == CPU_POWERPC_LOGICAL_2_05) ? 2050 : \
> -    ((cpuver) == CPU_POWERPC_LOGICAL_2_06) ? 2060 : \
> -    ((cpuver) == CPU_POWERPC_LOGICAL_2_06_PLUS) ? 2061 : \
> -    ((cpuver) == CPU_POWERPC_LOGICAL_2_07) ? 2070 : 0)
> -
> -static void cas_handle_compat_cpu(PowerPCCPUClass *pcc, uint32_t pvr,
> -                                  unsigned max_lvl, unsigned *compat_lvl,
> -                                  unsigned *compat_pvr)
> -{
> -    unsigned lvl = get_compat_level(pvr);
> -    bool is205, is206, is207;
> -
> -    if (!lvl) {
> -        return;
> -    }
> -
> -    /* If it is a logical PVR, try to determine the highest level */
> -    is205 = (pcc->pcr_supported & PCR_COMPAT_2_05) &&
> -            (lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_05));
> -    is206 = (pcc->pcr_supported & PCR_COMPAT_2_06) &&
> -            ((lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_06)) ||
> -             (lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_06_PLUS)));
> -    is207 = (pcc->pcr_supported & PCR_COMPAT_2_07) &&
> -            (lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_07));
> -
> -    if (is205 || is206 || is207) {
> -        if (!max_lvl) {
> -            /* User did not set the level, choose the highest */
> -            if (*compat_lvl <= lvl) {
> -                *compat_lvl = lvl;
> -                *compat_pvr = pvr;
> -            }
> -        } else if (max_lvl >= lvl) {
> -            /* User chose the level, don't set higher than this */
> -            *compat_lvl = lvl;
> -            *compat_pvr = pvr;
> -        }
> -    }
> -}
> -
> -static target_ulong h_client_architecture_support(PowerPCCPU *cpu_,
> +static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
>                                                    sPAPRMachineState *spapr,
>                                                    target_ulong opcode,
>                                                    target_ulong *args)
>  {
>      target_ulong list = ppc64_phys_to_real(args[0]);
>      target_ulong ov_table;
> -    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu_);
>      CPUState *cs;
> -    bool cpu_match = false;
> -    unsigned old_compat_pvr = cpu_->compat_pvr;
> -    unsigned compat_lvl = 0, compat_pvr = 0;
> -    unsigned max_lvl = get_compat_level(cpu_->max_compat);
> -    int counter;
> +    bool explicit_match = false; /* Matched the CPU's real PVR */
> +    uint32_t max_compat = cpu->max_compat;
> +    uint32_t best_compat = 0;
> +    int i;
>      sPAPROptionVector *ov5_guest, *ov5_cas_old, *ov5_updates;
> 
> -    /* Parse PVR list */
> -    for (counter = 0; counter < 512; ++counter) {
> +    /*
> +     * We scan the supplied table of PVRs looking for two things
> +     *   1. Is our real CPU PVR in the list?
> +     *   2. What's the "best" listed logical PVR
> +     */
> +    for (i = 0; i < 512; ++i) {
>          uint32_t pvr, pvr_mask;
> 
> -        pvr_mask = ldl_be_phys(&address_space_memory, list);
> -        list += 4;
>          pvr = ldl_be_phys(&address_space_memory, list);
> -        list += 4;
> -
> -        trace_spapr_cas_pvr_try(pvr);
> -        if (!max_lvl &&
> -            ((cpu_->env.spr[SPR_PVR] & pvr_mask) == (pvr & pvr_mask))) {
> -            cpu_match = true;
> -            compat_pvr = 0;
> -        } else if (pvr == cpu_->compat_pvr) {
> -            cpu_match = true;
> -            compat_pvr = cpu_->compat_pvr;
> -        } else if (!cpu_match) {
> -            cas_handle_compat_cpu(pcc, pvr, max_lvl, &compat_lvl, &compat_pvr);
> -        }
> -        /* Terminator record */
> +        pvr_mask = ldl_be_phys(&address_space_memory, list + 4);
> +        list += 8;
> +
>          if (~pvr_mask & pvr) {
> -            break;
> +            break; /* Terminator record */
>          }
> +
> +        if ((cpu->env.spr[SPR_PVR] & pvr_mask) == (pvr & pvr_mask)) {
> +            explicit_match = true;

The previous code only did this check if max_lvl/max_compat was set. I'm
not sure if it's possible in practice, but in theory this PVR might also
happen to be the next best_compat PVR, but since we test positive here
we may not not set best_compat accordingly.

> +        } else {
> +            if (ppc_check_compat(cpu, pvr, best_compat, max_compat)) {
> +                best_compat = pvr;
> +            }
> +        }
> +    }
> +
> +    if (!max_compat && explicit_match) {
> +        /* If the guest explicitly supports the CPU, *and* user hasn't
> +         * requested a compatibility mode, use "raw" mode */
> +        best_compat = 0;
> +    } else if (best_compat == 0) {
> +        /* Didn't find any supported compat modes */
> +        /* FIXME: what's the right error here? */
> +        return H_HARDWARE;
>      }
> 
>      /* Parsing finished */
> -    trace_spapr_cas_pvr(cpu_->compat_pvr, cpu_match,
> -                        compat_pvr, pcc->pcr_mask);
> +    trace_spapr_cas_pvr(cpu->compat_pvr, explicit_match, best_compat);
> 
>      /* Update CPUs */
> -    if (old_compat_pvr != compat_pvr) {
> +    if (cpu->compat_pvr != best_compat) {
>          CPU_FOREACH(cs) {
>              SetCompatState s = {
> -                .compat_pvr = compat_pvr,
> +                .compat_pvr = best_compat,
>                  .err = NULL,
>              };
> 
> diff --git a/hw/ppc/trace-events b/hw/ppc/trace-events
> index 2297ead..604ac92 100644
> --- a/hw/ppc/trace-events
> +++ b/hw/ppc/trace-events
> @@ -15,7 +15,7 @@ spapr_cas_continue(unsigned long n) "Copy changes to the guest: %ld bytes"
> 
>  # hw/ppc/spapr_hcall.c
>  spapr_cas_pvr_try(uint32_t pvr) "%x"
> -spapr_cas_pvr(uint32_t cur_pvr, bool cpu_match, uint32_t new_pvr, uint64_t pcr) "current=%x, cpu_match=%u, new=%x, compat flags=%"PRIx64
> +spapr_cas_pvr(uint32_t cur_pvr, bool explicit_match, uint32_t new_pvr) "current=%x, explicit_match=%u, new=%x"
> 
>  # hw/ppc/spapr_iommu.c
>  spapr_iommu_put(uint64_t liobn, uint64_t ioba, uint64_t tce, uint64_t ret) "liobn=%"PRIx64" ioba=0x%"PRIx64" tce=0x%"PRIx64" ret=%"PRId64
> -- 
> 2.7.4
>