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

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Oct 31, 2016 at 04:00:14PM +1100, Alexey Kardashevskiy wrote:
> On 30/10/16 22:12, David Gibson wrote:
> > 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);
> 
> 
> LoPAPR: List-entry = 4-byte-mask : 4-byte-PVR-value
> 
> This patch changes the order and "cas" fails.

Oops, yes, thanks for the catch.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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