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

[Alexey Kardashevskiy]

On 31/10/16 19:39, David Gibson wrote:
> On Mon, Oct 31, 2016 at 04:55:42PM +1100, Alexey Kardashevskiy wrote:
>> 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 <address@hidden>
>>> ---
>>>  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

In last 5+ years, I have never seen pointer compared anyhow but using "=="
and "!=". A bit unusual.


Reviewed-by: Alexey Kardashevskiy <address@hidden>





>>> +     */
>>>      { /* 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 ;)
> 
> For local variables, brevity is a virtue.





-- 
Alexey

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