Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw

[Paolo Bonzini]

Il 17/07/2013 17:50, Anthony Liguori ha scritto:
> Paolo Bonzini <address@hidden> writes:
> 
>> Il 17/07/2013 11:50, Markus Armbruster ha scritto:
>>> Richard Henderson <address@hidden> writes:
>>>
>>>> Honor the implementation maximum access size, and at least check
>>>> the minimum access size.
>>>>
>>>> Reviewed-by: Paolo Bonzini <address@hidden>
>>>> Signed-off-by: Richard Henderson <address@hidden>
>>>
>>> Fails for me:
>>>
>>> qemu-system-x86_64: /work/armbru/qemu/exec.c:1927: memory_access_size: 
>>> Assertion `l >= access_size_min' failed.
>>
>> This:
>>
>>     unsigned access_size_min = mr->ops->impl.min_access_size;
>>     unsigned access_size_max = mr->ops->impl.max_access_size;
>>
>> must be respectively:
>>
>>     unsigned access_size_min = 1;
>>     unsigned access_size_max = mr->ops->valid.max_access_size;
>>
>> access_size_min can be 1 because erroneous accesses must not crash 
>> QEMU, they should trigger exceptions in the guest or just return 
>> garbage (depending on the CPU).  I'm not sure I understand the comment, 
>> placing a 4-byte field at the last byte of a region makes no sense 
>> (unless impl.unaligned is true).
>>
>> access_size_max can be mr->ops->valid.max_access_size because memory.c 
>> can and will still break accesses bigger than 
>> mr->ops->impl.max_access_size.
>>
>> Markus, can you try the minimal patch above?  Or this one that also
>> does the consequent simplifications.
> 
> FYI, the reproducer is very simple:
> 
> qemu-system-x86_64 -usb

My patch works.

Paolo

> Regards,
> 
> Anthony Liguori
> 
>>
>> diff --git a/exec.c b/exec.c
>> index c99a883..0904283 100644
>> --- a/exec.c
>> +++ b/exec.c
>> @@ -1898,14 +1898,8 @@ static inline bool 
>> memory_access_is_direct(MemoryRegion *mr, bool is_write)
>>  
>>  static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
>>  {
>> -    unsigned access_size_min = mr->ops->impl.min_access_size;
>> -    unsigned access_size_max = mr->ops->impl.max_access_size;
>> +    unsigned access_size_max = mr->ops->valid.max_access_size;
>>  
>> -    /* Regions are assumed to support 1-4 byte accesses unless
>> -       otherwise specified.  */
>> -    if (access_size_min == 0) {
>> -        access_size_min = 1;
>> -    }
>>      if (access_size_max == 0) {
>>          access_size_max = 4;
>>      }
>> @@ -1922,9 +1916,6 @@ static int memory_access_size(MemoryRegion *mr, 
>> unsigned l, hwaddr addr)
>>      if (l > access_size_max) {
>>          l = access_size_max;
>>      }
>> -    /* ??? The users of this function are wrong, not supporting minimums 
>> larger
>> -       than the remaining length.  C.f. memory.c:access_with_adjusted_size. 
>>  */
>> -    assert(l >= access_size_min);
>>  
>>      return l;
>>  }
>>
>> Paolo
>