Re: [Xen-ia64-devel] Re: copying data to guest

[Jes Sorensen <jes@xxxxxxx>]

Tristan Gingold wrote:
>> - enhance fake SAL code in geust domain pseudo physical address space.
>>   Currently only break code is embedded.
>>   Make it smarter to handle virtual addresses.
>>   - convert virtual address into pseudo physical address
>>     and pass pseudo physical address to Xen.
>>   - use a predefined reserved area for SAL.
>>     (This requires domain builder change)
>>     It copies the data into the area, and call hypervisor.
>>     After the hypercall, it copies back data into virtual address.
>>     The tlb miss can be handled by OS.
> IMHO enhancing the SAL stubs is the right way.  We should convert virtual
> address and use xencomm.
> 
> Tristan.

Thought a bit more about this. I whipped up some code last week that
relied on the 1:1 mapping knowledge which you don't like. I agree it's
not ideal, however we have a real issue with the fact that some current
SAL calls expect a kernel virtual address. We simply won't be able to
provide full VT support if we cannot come up with a way to do this in
a reliable manner :(

I may be able to convince our PROM team to change the SAL calls that are
SN2 specific to take physical addresses. However even when taking
physical (or metaphysical addresses) can we reliably access the memory?
I presume we can? But what about the generic calls?

Xencomm is fine for dom0 stuff, but not for domUs. Well fine is a
relative term here, the Xencomm API is probably the most ugly part of
Xen I have come across so far :(

Cheers,
Jes

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