Re: [PATCH] slow_map: minor improvements to ROM BAR handling

Alexander Graf
2009-12-22T15:41:08Z

Avi Kivity wrote:
> On 12/22/2009 05:36 PM, Alexander Graf wrote:
>>
>>> Is there a way to trap this and fprintf something?
>>>
>> I don't think so. KVM will just trap on execution outside of RAM and
>> either fail badly or throw something bad into the guest. MMIO access
>> works by analyzing the instruction that accesses the MMIO address. That
>> just doesn't work when we don't have an instruction to analyze.
>>
>
> We could certainly extend emulate.c to fetch instruction bytes from
> userspace. It uses ->read_std() now, so we'd need to switch to
> ->read_emulated() and add appropriate buffering.

I thought the policy on emulate.c was to not have a full instruction
emulator but only emulate instructions that do PT modifications or MMIO
access?

Btw, we're in the same situation with PowerPC here. The instruction
emulator is _really_ small. It only does a few MMU specific
instructions, a couple of privileged ones and MMIO accessing ones.

Alex