Re: PowerPC page faults

Anthony Liguori
2009-05-11T22:18:14Z

Hollis Blanchard wrote:
> On Mon, 2009-05-11 at 12:54 -0500, Anthony Liguori wrote:
>
>> For future ppcemb's, do you know if there is an equivalent of a PF exit
>> type? Does the hardware squirrel away the faulting address somewhere
>> and set PC to the start of the instruction? If so, no guest memory load
>> should be required.
>>
>
> Ahhh... you're saying that the address itself (or offset within a page)
> is the hypercall token, totally separate from IO emulation, and so we
> could ignore the access size.

No, I'm not being nearly that clever.

I was suggesting that hardware virtualization support in future PPC
systems might contain a mechanism to intercept a guest-mode TLB miss.
If it did, it would be useful if that guest-mode TLB miss "exit"
contained extra information somewhere that included the PC of the
faulting instruction, the address response for the fault, and enough
information to handle the fault without instruction decoding.

I assume all MMIO comes from the same set of instructions in PPC?
Something like ld/st instructions? Presumably all you need to know from
instruction decoding is the destination register and whether it was a
read or write?

Or am I oversimplifying? Does the current hardware spec contain this
sort of assistance?

Regards,

Anthony Liguori