SIMPLE??????????? SOUNDS LIKE GREEK! lol Actually.. thats scary that I
followed the conversation! lol
I am assuming MMIO = memory mapped input output?
I don't know about the rest of you but I want to be as smart as Ramon and
Kevin one day!
Nick
----- Original Message -----
From: "Ramon van Handel" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Saturday, December 16, 2000 4:53 AM
Subject: Re: [plex86] Performance enhancement: elminiating mode and context
switches
> On Fri, 15 Dec 2000, Kevin Lawton wrote:
> > Running guest ring0 code at ring0 open memory access to PTE.P==1 pages,
> > which includes the monitor interrupt handlers, and monitor data
> > structures. Thus, all memory access instructions would be dangerous.
> > We'd have to move to the concept of 'shortening' guest kernel segments,
> > so we leave our selves a safe hole to put the monitor in.
>
> You need to prescan memory accesses anyway in order to catch
> MMIO. You don't need to emulate non-MMIO memory acesses, but you can keep
> the monitor in the same place and simply change the address (the size of
> the memory access instruction will remain the same anyway.)
>
> > Once you modify the instructions in a page by extending the size
> > of an instruction (changing an IO to a call), as opposed to
> > inserting an INT3 (always 1 byte), we have to move from our notion
> > of simple modified cache pages to a more dynamic translation like
> > scheme. The branch offsets change etc.
>
> No, not necessarily. What you do is overwrite the next instruction and
> keep the original in a branch table. You use a call to go to the
> emulation routine; in stead of using ret, however, the emulation routine
> will look in the branch table, which contains (1) the next instructions to
> be executed, and (2) the address of the first instruction that was not
> overwritten.
>
> It's simple really, perhaps I should make a little graphic description of
> the process?
>
> -- Ramon
>
>
>
