Gleb Natapov wrote:
On Wed, Mar 10, 2010 at 07:08:31PM +0900, Takuya Yoshikawa wrote:
Gleb Natapov wrote:
Entering guest from time to time will not change semantics of the
processor (if code is not modified under processor's feet at least).
Currently we reenter guest mode after each iteration of string
instruction for all instruction but ins/outs.
E.g., is there no chance that during the repetitions, in the middle of the
repetitions, page faults occur? If it can, without entering the guest, can
we handle it?
-- I lack some basic assumptions?
If page fault occurs we inject it to the guest.
Oh, I maight fail to tell what I worried about.
Opposite, I mean, I worried about NOT reentering the guest case.
Are you thinking about something specific here? If we inject exceptions
Yes.
when they occur and we inject interrupt when they arrive what problem do
you see? I guess this is how real CPU actually works. I doubt it
re-reads string instruction on each iteration.
No problem if we detect and inject page faults like that.
I just didn't so certain that when we encounter a page fault in the middle
of the repetitions(about rep specific case), if we can inject it, suspend the
repetition and enter the guest immediately like SDM Vol.2B says:
"A repeating string operation can be suspended by an exception or interrupt.
When this happens, the state of the registers is preserved to allow the string
operation to be resumed upon a return from the exception or interrupt handler.
...
This mechanism allows long string operations to proceed without affecting the
interrupt response time of the system."
Ah, I might misunderstand that if we reenter the guest every time for rep,
page fault detection, not injection, can be done by the other ways easily,
by EXIT reason or something. Both ways may need the same thing, sorry.
Another concern I wrote was just about the dependencies between your
"time to time" criteria and SDM's "without affecting the interrupt response time".
This is just the problem of how we can determine the criteria appropriately.
I know that current implementation with reentrance is OK.
Current implementation does not reenter guest on each iteration for pio
string, so currently we have both variants.
I'm sorry, I was confused as if the current implementation already
included some of your patches.
To inject a page fault without reentering the guest, we need to add
some more hacks to the emulator IIUC.
No, we just need to enter guest if exception happens. I see that this in
handled incorrectly in my current patch series.
I was just not certain if the following condition(from SDM Vol.2B) is satisfied
"The source and destination registers point to the next string elements
to be operated on, the EIP register points to the string instruction,
and the ECX register has the value it held following the last successful
iteration of the instruction."
in the emulator's fault handling. I should have read your patch more closely.
Thanks,
Takuya
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
