Re: [Qemu-devel] [RFC v1] Add declarations for hierarchical memory region API

[Avi Kivity <avi@redhat.com>]

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.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.