Re: [PATCH][RESEND] x86_emulator: Emulate cld and std instruction

[Andrea Arcangeli <andrea@qumranet.com>]

On Thu, Jul 31, 2008 at 01:25:40PM +0300, Mohammed Gamal wrote:
> The only check was if CS RPL equals SS RPL, so what happens is that
> when a vmexit and then a vmentry occurs CS and SS RPL maybe equal, but

Yes same problem here, vmentry fails because CS is set to >16 bit
value (I think) but the last two bits of CS and SS are the same. That
surely is the wrong check to know if we've to invoke emulation on
vmentry failure.

> other checks might cause a vmentry failure. I've written a function to
> check that guest state is VMX valid - although not all checks are
> implemented yet, and I no more get the occasional vmexits.

Can you send me your latest patch so I can test. I tried to force
unconditional emulation on invalid guest state exception generated by
vmentry failure but even emulation fails for me, and then your patch
sets SS to sane value but that's meaningless here as it's CS that is
set to >16bit value. I've yet to trace where emulation fails, but I
suspect it's fetching instructions from the wrong place by not
emulating the segment-caches set by protected mode, maybe not.