Avi Kivity wrote: > Anthony Liguori wrote: >> Jun Koi wrote: >> >>> On 10/1/07, Anthony Liguori <[EMAIL PROTECTED]> wrote: >>> >>>> Cameron Macdonell wrote: >>>> >>>>> Hi, >>>>> >>>>> I'm trying to understand guest virtualization at the lower levels. I >>>>> have a somewhat basic question: How does KVM virtualize an int80 >>>>> instruction from a guest? A pointer to an answer is just as good as >>>>> an answer itself. >>>>> >>>>> >>>> The same thing happens as it does on normal hardware. >>>> >>>> The way VT/SVM works (at a high level), is that certain >>>> instructions and >>>> events check a special area called the VMCS/VMCB to determine whether >>>> the event should generate a vmexit which is really just a special type >>>> of trap. >>>> >>>> There are no hooks for interrupts 32-255 so the hardware operates >>>> as it >>>> normally would. If you're interested in getting a trap for int80 >>>> within >>>> KVM, you'll have to trap sidt/lidt and virtualize the IDT. You'll >>>> need >>>> to setup a fake IDT and have the int80 handler do a hypercall. >>>> This is >>>> complicated if the guest is using a fast-syscall mechanism. It may >>>> be a >>>> little challenging finding a piece of guest memory to take over >>>> that has >>>> a valid virtual mapping. >>>> >>> This is a bit vague to me. Why do you need "a piece of guest memory" >>> here? >>> >> >> You don't just need guest memory, you need a valid guest virtual >> address too. The IDTR contains a guest VA. If you want to create >> your own IDT, then it has to be a valid VA in the guest's address space. >> >> > > You can set the guest idt size to zero and trap the double fault > exception.
You could, but then you're trapping all exceptions instead of just the int80. Of course, int80 is probably the one you care most about performance wise so it's probably a reasonable approach. Regards, Anthony Liguori ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kvm-devel
