Re: [Qemu-devel] [RFC 09/17] ppc: Validate compatibility modes when setting

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 30/10/16 22:12, David Gibson wrote:
> Current ppc_set_compat() will attempt to set any compatiblity mode
> specified, regardless of whether it's available on the CPU.  The caller is
> expected to make sure it is setting a possible mode, which is awkwward
> because most of the information to make that decision is at the CPU level.
> 
> This begins to clean this up by introducing a ppc_check_compat() function
> which will determine if a given compatiblity mode is supported on a CPU
> (and also whether it lies within specified minimum and maximum compat
> levels, which will be useful later).  It also contains an assertion that
> the CPU has a "virtual hypervisor"[1], that is, that the guest isn't
> permitted to execute hypervisor privilege code.  Without that, the guest
> would own the PCR and so could override any mode set here.  Only machine
> types which use a virtual hypervisor (i.e. 'pseries') should use
> ppc_check_compat().
> 
> ppc_set_compat() is modified to validate the compatibility mode it is given
> and fail if it's not available on this CPU.
> 
> [1] Or user-only mode, which also obviously doesn't allow access to the
> hypervisor privileged PCR.  We don't use that now, but could in future.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  target-ppc/compat.c | 41 +++++++++++++++++++++++++++++++++++++++++
>  target-ppc/cpu.h    |  2 ++
>  2 files changed, 43 insertions(+)
> 
> diff --git a/target-ppc/compat.c b/target-ppc/compat.c
> index 66529a6..1059555 100644
> --- a/target-ppc/compat.c
> +++ b/target-ppc/compat.c
> @@ -28,29 +28,37 @@
>  typedef struct {
>      uint32_t pvr;
>      uint64_t pcr;
> +    uint64_t pcr_level;
>      int max_threads;
>  } CompatInfo;
>  
>  static const CompatInfo compat_table[] = {
> +    /*
> +     * Ordered from oldest to newest - the code relies on this
> +     */
>      { /* POWER6, ISA2.05 */
>          .pvr = CPU_POWERPC_LOGICAL_2_05,
>          .pcr = PCR_COMPAT_2_07 | PCR_COMPAT_2_06 | PCR_COMPAT_2_05
>                 | PCR_TM_DIS | PCR_VSX_DIS,
> +        .pcr_level = PCR_COMPAT_2_05,
>          .max_threads = 2,
>      },
>      { /* POWER7, ISA2.06 */
>          .pvr = CPU_POWERPC_LOGICAL_2_06,
>          .pcr = PCR_COMPAT_2_07 | PCR_COMPAT_2_06 | PCR_TM_DIS,
> +        .pcr_level = PCR_COMPAT_2_06,
>          .max_threads = 4,
>      },
>      {
>          .pvr = CPU_POWERPC_LOGICAL_2_06_PLUS,
>          .pcr = PCR_COMPAT_2_07 | PCR_COMPAT_2_06 | PCR_TM_DIS,
> +        .pcr_level = PCR_COMPAT_2_06,
>          .max_threads = 4,
>      },
>      { /* POWER8, ISA2.07 */
>          .pvr = CPU_POWERPC_LOGICAL_2_07,
>          .pcr = PCR_COMPAT_2_07,
> +        .pcr_level = PCR_COMPAT_2_07,
>          .max_threads = 8,
>      },
>  };
> @@ -67,6 +75,35 @@ static const CompatInfo *compat_by_pvr(uint32_t pvr)
>      return NULL;
>  }
>  
> +bool ppc_check_compat(PowerPCCPU *cpu, uint32_t compat_pvr,
> +                      uint32_t min_compat_pvr, uint32_t max_compat_pvr)
> +{
> +    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
> +    const CompatInfo *compat = compat_by_pvr(compat_pvr);
> +    const CompatInfo *min = compat_by_pvr(min_compat_pvr);
> +    const CompatInfo *max = compat_by_pvr(max_compat_pvr);


You keep giving very generic names (as "min" and "max") to local variables ;)


> +
> +#if !defined(CONFIG_USER_ONLY)
> +    g_assert(cpu->vhyp);
> +#endif
> +    g_assert(!min_compat_pvr || min);
> +    g_assert(!max_compat_pvr || max);
> +
> +    if (!compat) {
> +        /* Not a recognized logical PVR */
> +        return false;
> +    }
> +    if ((min && (compat < min)) || (max && (compat > max))) {
> +        /* Outside specified range */
> +        return false;
> +    }
> +    if (!(pcc->pcr_supported & compat->pcr_level)) {
> +        /* Not supported by this CPU */
> +        return false;
> +    }
> +    return true;
> +}
> +
>  void ppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr, Error **errp)
>  {
>      const CompatInfo *compat = compat_by_pvr(compat_pvr);
> @@ -79,6 +116,10 @@ void ppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr, Error **errp)
>      } else if (!compat) {
>          error_setg(errp, "Unknown compatibility PVR 0x%08"PRIx32, compat_pvr);
>          return;
> +    } else if (!ppc_check_compat(cpu, compat_pvr, 0, 0)) {
> +        error_setg(errp, "Compatibility PVR 0x%08"PRIx32" not valid for CPU",
> +                   compat_pvr);
> +        return;
>      } else {
>          pcr = compat->pcr;
>      }
> diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
> index cfda7b2..91e8be8 100644
> --- a/target-ppc/cpu.h
> +++ b/target-ppc/cpu.h
> @@ -1314,6 +1314,8 @@ static inline int cpu_mmu_index (CPUPPCState *env, bool ifetch)
>  
>  /* Compatibility modes */
>  #if defined(TARGET_PPC64)
> +bool ppc_check_compat(PowerPCCPU *cpu, uint32_t compat_pvr,
> +                      uint32_t min_compat_pvr, uint32_t max_compat_pvr);
>  void ppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr, Error **errp);
>  int ppc_compat_max_threads(PowerPCCPU *cpu);
>  #endif /* defined(TARGET_PPC64) */
> 


-- 
Alexey