On 25/04/2019 00:43, Mathieu Tarral wrote: > On Wednesday 24 April 2019 14:00, Andrew Cooper <andrew.coop...@citrix.com> > wrote: > >> On 23/04/2019 22:59, Mathieu Tarral wrote: >> >>>>> The funny thing is that it's always at the same instruction that it >>>>> fails, the 106th singlestep, >>>>> at 0x806d32dc: >>>>> [0x7c90e514]> s 0x806d32dc >>>>> [0x806d32dc]> pd 10 >>>>> 0x806d32dc 890d8000feff mov dword [0xfffe0080], ecx >>>>> This is a read of the APIC TPR, which is very commonly an operation >>>>> accelerated by hardware (because without it, virtualising windows XP is >>>>> exceedingly slow). >>>> What is your CPU, and how exactly are you trying to singlestep. Is it >>>> with MTF, or using the trap flag inside the guest? >>>> My CPU is an Intel i7-8750H. >>>> I'm using the libvmi API, which is enabling the MTF flag to singlestep, if >>>> i judge by the debug logs. >> Ok - that is a CoffeeLake. >> >> I've had a quick play with a simple example (XTF test and xen-access) >> and MTF does appear to work fine with both TPR shadowing and full APIC >> virtualisation. I've tried on Haswell, KabyLake and CoffeeLake. > Thank you for testing. > >> Can you describe the exact VMI configuration you've got enabled - >> specifically which other intercepts are active? > My BreakpointManager class is dealing with VMI events. > It registers 3 events: > - int3 > - debug event (for hardware breakpoints) > - singlestep event (for breakpoint recoil on int3) > > https://github.com/Wenzel/pyvmidbg/blob/1a2e97c238a96c98c19cdbbdefa6047be246e504/vmidbg/breakpoint.py#L20
What about control register intercepts, or memory permission restrictions? I expect things are going wrong when the TPR access is emulated by Xen, rather than completed directly by hardware, but I can't explain how you'd be getting into that situation without some other VMI settings being active at the same time. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
