Jan Kiszka wrote: > Avi Kivity wrote: > >> Jan Kiszka wrote: >> >>> This still leaves me with the question how to handle the case when the >>> host sets and arms some debug registers to debug the guest and the >>> latter does the same to debug itself. Guest access will be trapped, OK, >>> but KVM will then have to decide which value should actually be >>> transfered into the registers. Hmm, does SVM virtualizes all debug >>> registers, leaving the real ones to the host? >>> >>> >> There's no way this can work. There are still only four debug >> registers, and the guest and host together can ask for eight different >> addresses. It is theoretically doable by hiding all mappings to pages >> that are debug targets, but it would probably double the kvm code size. >> >> A good short-term compomise is to abort if the guest starts using >> enabling a debug address register. A better solution might be to place >> host debug addresses into unused guest debug registers, so that as long >> as nr_guest_debug + nr_host_debug <= 4, we can still proceed. >> > > I tried the latter, but we cannot cleanly share DR7 between both users. >
I actually think we can, but... > Thus I'm now going for a prioritized approach: debug register will stop > to have any effect for the guest as soon as the host starts to use them. > That's far simpler the implement and also easier to understand for the user. > > Agreed, having a simple model is preferred here, both from the user's point of view and from a code complexity point of view. If you're debugging a debugger use plain qemu. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
