Re: [Qemu-devel] [RFC 0/5] execute code from mmio area

[Frederic Konrad]

On 02/04/2017 01:33 PM, Peter Maydell wrote:
> On 3 February 2017 at 17:06,  <address@hidden> wrote:
>> From: KONRAD Frederic <address@hidden>
>>
>> This patch-set allows to execute code from mmio areas.
>> The main goal of this is to be able to run code for example from an SPI 
>> device.
>>
>> The three first patch fixes the way get_page_addr_code fills the TLB.
>>
>> The fourth patch implements the mmio execution helpers: the device must
>> implement the request_ptr callback of the MemoryRegion and will be notified 
>> when
>> the guest wants to execute code from it.
>>
>> The fifth patch implements the execution from the SPI memories in the
>> xilinx_spips model.
> 
> I like the general idea, but there's an awkward issue:
> at the moment our translation system assumes that when we're
> translating code then if the first instruction in the TB
> can be read OK then we won't ever get a fault trying to
> read subsequent bytes up to the end of the page. If we
> move from "we only translate code out of whole pages of
> RAM" to "we might translate code out of devices that
> are in subpages" then this assumption gets broken.
> (The symptom would be that we would report the fault
> in the wrong place, for the PC at the start of the TB.)
> 
> thanks
> -- PMM
> 

Hi Peter,

I think I see your point.
Is that the case that we might get a Bad RAM address error or some such
if we are not on a page boundary (or too small as you say)?
I guess this is a limitation. Mapping on a page boundary shouldn't be
too much restrictive.

Thanks,
Fred