On 2014-03-09 09:11, Jan Kiszka wrote: > On 2014-03-07 12:42, Paolo Bonzini wrote: >> Alex Williamson reported that a Windows game does something weird that >> makes the guest save and restore debug registers on each context switch. >> This cause several hundred thousands vmexits per second, and basically >> cuts performance in half when running under KVM. >> >> However, when not running in guest-debug mode, the guest controls the >> debug registers and having to take an exit for each DR access is a waste >> of time. We just need one vmexit to load any stale values of DR0-DR6, >> and then we can let the guest run freely. On the next vmexit (whatever >> the reason) we will read out whatever changes the guest made to the >> debug registers. >> >> Tested with x86/debug.flat on both Intel and AMD, both direct and >> nested virtualization. >> >> Changes from RFC: changed get_dr7 callback to sync_dirty_debug_regs, >> new patches 5-7. > > This looks good now to me from KVM perspective. I was just wondering how > the case is handled that the host used debug registers on the thread the > runs a VCPU? What if I set a hw breakpoint on its userspace path e.g.? > What if I debug the kernel side with kgdb? Ah, this part didn't change, we still switch between host and guest state on vmentries/exits. All fine! Jan
Attachment:
signature.asc
Description: OpenPGP digital signature
