Re: [Qemu-devel] [PATCHv2 2/3] target-ppc: Add helpers for updating a CPU's SDR1 and external HPT

[David Gibson]

On Tue, Mar 22, 2016 at 05:33:45PM +0100, Laurent Vivier wrote:
> Hi David,
> 
> using kvm-unit-tests, I've found a side effect of your patches: the MSR
> is cleared (and perhaps some others).
> 
> I was trying to test my patch on top of QEMU master:
> 
> "ppc64: set MSR_SF bit"
> http://patchwork.ozlabs.org/patch/598198/
> 
> and it was not working anymore.
> 
> By bisecting, I've found this commit.
> 
> I think "cpu_synchronize_state()" in "ppc_hash64_set_external_hpt()"
> restores the MSR from KVM whereas the one from QEMU has not been saved,
> because cpu_synchronize_all_post_reset() is called later.
> 
> So it is cleared.
> 
> You can test this by applying the MSR_SF patch and using the "emulator"
> test of kvm-unit-tests (the "emulator: 64bit" test case)

Ugh, you're right of course.  But, I'm having a bit of trouble
figuring out how to fix it propertly.

> 
> Laurent
> 
> On 07/03/2016 03:26, David Gibson wrote:
> > When a Power cpu with 64-bit hash MMU has it's hash page table (HPT)
> > pointer updated by a write to the SDR1 register we need to update some
> > derived variables.  Likewise, when the cpu is configured for an external
> > HPT (one not in the guest memory space) some derived variables need to be
> > updated.
> > 
> > Currently the logic for this is (partially) duplicated in ppc_store_sdr1()
> > and in spapr_cpu_reset().  In future we're going to need it in some other
> > places, so make some common helpers for this update.
> > 
> > In addition the new ppc_hash64_set_external_hpt() helper also updates
> > SDR1 in KVM - it's not updated by the normal runtime KVM <-> qemu CPU
> > synchronization.  In a sense this belongs logically in the
> > ppc_hash64_set_sdr1() helper, but that is called from
> > kvm_arch_get_registers() so can't itself call cpu_synchronize_state()
> > without infinite recursion.  In practice this doesn't matter because
> > the only other caller is TCG specific.
> > 
> > Currently there aren't situations where updating SDR1 at runtime in KVM
> > matters, but there are going to be in future.
> > 
> > Signed-off-by: David Gibson <address@hidden>
> > ---
> >  hw/ppc/spapr.c          | 13 ++-----------
> >  target-ppc/kvm.c        |  2 +-
> >  target-ppc/kvm_ppc.h    |  6 ++++++
> >  target-ppc/mmu-hash64.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> >  target-ppc/mmu-hash64.h |  6 ++++++
> >  target-ppc/mmu_helper.c | 13 ++++++-------
> >  6 files changed, 64 insertions(+), 19 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 64c4acc..72a018b 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -1196,17 +1196,8 @@ static void spapr_cpu_reset(void *opaque)
> >  
> >      env->spr[SPR_HIOR] = 0;
> >  
> > -    env->external_htab = (uint8_t *)spapr->htab;
> > -    env->htab_base = -1;
> > -    /*
> > -     * htab_mask is the mask used to normalize hash value to PTEG index.
> > -     * htab_shift is log2 of hash table size.
> > -     * We have 8 hpte per group, and each hpte is 16 bytes.
> > -     * ie have 128 bytes per hpte entry.
> > -     */
> > -    env->htab_mask = (1ULL << (spapr->htab_shift - 7)) - 1;
> > -    env->spr[SPR_SDR1] = (target_ulong)(uintptr_t)spapr->htab |
> > -        (spapr->htab_shift - 18);
> > +    ppc_hash64_set_external_hpt(cpu, spapr->htab, spapr->htab_shift,
> > +                                &error_fatal);
> >  }
> >  
> >  static void spapr_create_nvram(sPAPRMachineState *spapr)
> > diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
> > index 8a762e8..380dff6 100644
> > --- a/target-ppc/kvm.c
> > +++ b/target-ppc/kvm.c
> > @@ -867,7 +867,7 @@ static int kvm_put_vpa(CPUState *cs)
> >  }
> >  #endif /* TARGET_PPC64 */
> >  
> > -static int kvmppc_put_books_sregs(PowerPCCPU *cpu)
> > +int kvmppc_put_books_sregs(PowerPCCPU *cpu)
> >  {
> >      CPUPPCState *env = &cpu->env;
> >      struct kvm_sregs sregs;
> > diff --git a/target-ppc/kvm_ppc.h b/target-ppc/kvm_ppc.h
> > index fd64c44..fc79312 100644
> > --- a/target-ppc/kvm_ppc.h
> > +++ b/target-ppc/kvm_ppc.h
> > @@ -55,6 +55,7 @@ void kvmppc_hash64_write_pte(CPUPPCState *env, 
> > target_ulong pte_index,
> >                               target_ulong pte0, target_ulong pte1);
> >  bool kvmppc_has_cap_fixup_hcalls(void);
> >  int kvmppc_enable_hwrng(void);
> > +int kvmppc_put_books_sregs(PowerPCCPU *cpu);
> >  
> >  #else
> >  
> > @@ -246,6 +247,11 @@ static inline int kvmppc_enable_hwrng(void)
> >  {
> >      return -1;
> >  }
> > +
> > +static inline int kvmppc_put_books_sregs(PowerPCCPU *cpu)
> > +{
> > +    abort();
> > +}
> >  #endif
> >  
> >  #ifndef CONFIG_KVM
> > diff --git a/target-ppc/mmu-hash64.c b/target-ppc/mmu-hash64.c
> > index 9c58fbf..7b5200b 100644
> > --- a/target-ppc/mmu-hash64.c
> > +++ b/target-ppc/mmu-hash64.c
> > @@ -258,6 +258,49 @@ target_ulong helper_load_slb_vsid(CPUPPCState *env, 
> > target_ulong rb)
> >  /*
> >   * 64-bit hash table MMU handling
> >   */
> > +void ppc_hash64_set_sdr1(PowerPCCPU *cpu, target_ulong value,
> > +                         Error **errp)
> > +{
> > +    CPUPPCState *env = &cpu->env;
> > +    target_ulong htabsize = value & SDR_64_HTABSIZE;
> > +
> > +    env->spr[SPR_SDR1] = value;
> > +    if (htabsize > 28) {
> > +        error_setg(errp,
> > +                   "Invalid HTABSIZE 0x" TARGET_FMT_lx" stored in SDR1",
> > +                   htabsize);
> > +        htabsize = 28;
> > +    }
> > +    env->htab_mask = (1ULL << (htabsize + 18 - 7)) - 1;
> > +    env->htab_base = value & SDR_64_HTABORG;
> > +}
> > +
> > +void ppc_hash64_set_external_hpt(PowerPCCPU *cpu, void *hpt, int shift,
> > +                                 Error **errp)
> > +{
> > +    CPUPPCState *env = &cpu->env;
> > +    Error *local_err = NULL;
> > +
> > +    cpu_synchronize_state(CPU(cpu));
> > +
> > +    env->external_htab = hpt;
> > +    ppc_hash64_set_sdr1(cpu, (target_ulong)(uintptr_t)hpt | (shift - 18),
> > +                        &local_err);
> > +    if (local_err) {
> > +        error_propagate(errp, local_err);
> > +        return;
> > +    }
> > +
> > +    /* Not strictly necessary, but makes it clearer that an external
> > +     * htab is in use when debugging */
> > +    env->htab_base = -1;
> > +
> > +    if (kvm_enabled()) {
> > +        if (kvmppc_put_books_sregs(cpu) < 0) {
> > +            error_setg(errp, "Unable to update SDR1 in KVM");
> > +        }
> > +    }
> > +}
> >  
> >  static int ppc_hash64_pte_prot(PowerPCCPU *cpu,
> >                                 ppc_slb_t *slb, ppc_hash_pte64_t pte)
> > diff --git a/target-ppc/mmu-hash64.h b/target-ppc/mmu-hash64.h
> > index e7d9925..138cd7e 100644
> > --- a/target-ppc/mmu-hash64.h
> > +++ b/target-ppc/mmu-hash64.h
> > @@ -92,6 +92,12 @@ unsigned ppc_hash64_hpte_page_shift_noslb(PowerPCCPU 
> > *cpu,
> >  
> >  
> >  extern bool kvmppc_kern_htab;
> > +
> > +void ppc_hash64_set_sdr1(PowerPCCPU *cpu, target_ulong value,
> > +                         Error **errp);
> > +void ppc_hash64_set_external_hpt(PowerPCCPU *cpu, void *hpt, int shift,
> > +                                 Error **errp);
> > +
> >  uint64_t ppc_hash64_start_access(PowerPCCPU *cpu, target_ulong pte_index);
> >  void ppc_hash64_stop_access(uint64_t token);
> >  
> > diff --git a/target-ppc/mmu_helper.c b/target-ppc/mmu_helper.c
> > index e5ec8d6..fcb2cc5 100644
> > --- a/target-ppc/mmu_helper.c
> > +++ b/target-ppc/mmu_helper.c
> > @@ -2005,15 +2005,14 @@ void ppc_store_sdr1(CPUPPCState *env, target_ulong 
> > value)
> >      env->spr[SPR_SDR1] = value;
> >  #if defined(TARGET_PPC64)
> >      if (env->mmu_model & POWERPC_MMU_64) {
> > -        target_ulong htabsize = value & SDR_64_HTABSIZE;
> > +        PowerPCCPU *cpu = ppc_env_get_cpu(env);
> > +        Error *local_err = NULL;
> >  
> > -        if (htabsize > 28) {
> > -            fprintf(stderr, "Invalid HTABSIZE 0x" TARGET_FMT_lx
> > -                    " stored in SDR1\n", htabsize);
> > -            htabsize = 28;
> > +        ppc_hash64_set_sdr1(cpu, value, &local_err);
> > +        if (local_err) {
> > +            error_report_err(local_err);
> > +            error_free(local_err);
> >          }
> > -        env->htab_mask = (1ULL << (htabsize + 18 - 7)) - 1;
> > -        env->htab_base = value & SDR_64_HTABORG;
> >      } else
> >  #endif /* defined(TARGET_PPC64) */
> >      {
> > 
> 

-- 
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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