Guillaume Thouvenin wrote:
> On Mon, 18 Feb 2008 10:39:31 +0100
> Alexander Graf <[EMAIL PROTECTED]> wrote:
>
>
>
>>> So if you want to see a VMentry failure, just remove the SS patching
>>> and you'll see one. My guess would be that you see a lot of problems
>>> with otherwise working code too then, though, as SS can be anything in
>>> that state.
>>>
>
> So I made some tests and you were right, removing the SS patching
> showed VM entry failure but it also generated lots of problems. Thus I
> tried to modify a little bit the code and with the following patch (see
> the end of the email) I can detect VM Entry failures without generating
> other problems. It works when you use a distribution that is
> "big-real-mode free". I pasted the patch just to show the idea.
>
> It's interesting because we can continue to use the virtual mode for the
> majority of distribution and we can detect when a VM entry failure is
> detected it means that we need to switch from virtual mode to full real
> mode emulation. Such failure is caught in handle_vmentry_failure() when
> patch applied. If it's doable, the next step is the modification of the
> SS segment selector to succeed the vm-entry and the switch from virtual
> mode to a real mode emulation that could be done in
> handle_vmentry_failure(). Does it make sense?
>
>
Yes. An alternative (useful if a failed vmentry corrupts the guest
state) is to check all register state when switching modes.
> -
> + fix_rmode_seg(VCPU_SREG_CS, &vcpu->arch.rmode.cs);
> fix_rmode_seg(VCPU_SREG_ES, &vcpu->arch.rmode.es);
> fix_rmode_seg(VCPU_SREG_DS, &vcpu->arch.rmode.ds);
> fix_rmode_seg(VCPU_SREG_GS, &vcpu->arch.rmode.gs);
> fix_rmode_seg(VCPU_SREG_FS, &vcpu->arch.rmode.fs);
> + fix_rmode_seg(VCPU_SREG_SS, &vcpu->arch.rmode.ss);
>
Ideally you wouldn't call fix_rmode_seg() at all. The guest will
emulate until such time as the segments are valid for v8086, for example
when the guest reloads them itself.
> + switch (basic_exit_reason) {
> + case EXIT_REASON_INVALID_GUEST_STATE:
> + printk("caused by invalid guest state (%ld).\n",
> exit_qualification);
> + /* At this point we need to modify SS selector to pass
> vmentry test.
> + * This modification prevent the usage of virtual mode
> to emulate real
> + * mode so we need to pass in big real mode emulation
> + * with somehting like:
> + * vcpu->arch.rmode.emulate = 1
>
Note you might need to emulate in protected mode as well, for a small
part of the switch, for similar reasons.
--
error compiling committee.c: too many arguments to function
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