On 05/20/2011 02:23 AM, Avi Kivity wrote:
> On 05/19/2011 11:43 PM, Anthony Liguori wrote:
>> On 05/19/2011 09:12 AM, Avi Kivity wrote:
>>> The memory API separates the attributes of a memory region (its size, how
>>> reads or writes are handled, dirty logging, and coalescing) from where it
>>> is mapped and whether it is enabled. This allows a device to configure
>>> a memory region once, then hand it off to its parent bus to map it according
>>> to the bus configuration.
>>>
>>> Hierarchical registration also allows a device to compose a region out of
>>> a number of sub-regions with different properties; for example some may be
>>> RAM while others may be MMIO.
>>>
>>> + struct {
>>> + /* If nonzero, specify bounds on access sizes beyond which a
>>> machine
>>> + * check is thrown.
>>> + */
>>> + unsigned min_access_size;
>>> + unsigned max_access_size;
>>> + /* If true, unaligned accesses are supported. Otherwise unaligned
>>> + * accesses throw machine checks.
>>> + */
>>> + bool unaligned;
>>> + } valid;
>>
>> Under what circumstances would this be used?
>>
>> The behavior of devices that receive non-natural accesses varies wildly.
>>
>> For PCI devices, invalid accesses almost always return ~0. I can't think of
>> a device where an MCE would occur.
>
> This was requested by Richard, so I'll let him comment.
>
Several alpha system chips MCE when accessed with incorrect sizes.
E.g. only 64-bit accesses are allowed.
Is this structure honestly any better than 4 function pointers?
I can't see that it is, myself.
r~
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