[Qemu-devel] Re: [PATCH 4/4] KVM: Rework of guest debug state writing

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Feb 04, 2010 at 08:21:08PM +0100, Jan Kiszka wrote:
> Jan Kiszka wrote:
> > Marcelo Tosatti wrote:
> >> With kvm-autotest the failure is not sporadic (and the above commit
> >> applied): with KVM_SET_GUEST_DEBUG in arch_put_regs all migration 
> >> tests fail, without, all of them succeed. 
> >>
> >> So env->kvm_guest_debug has been zeroed by cpu_x86_init, which means
> >> the writeback via KVM_SET_GUEST_DEBUG does almost nothing. It does
> >> get_rflags and set_rflags in the kernel.
> > 
> > Hmm, it also copies debug regs around... BTW, where do we save/restore
> > dr0..7 between kernel and user space?
> > 
> > But that should not be a problem, both shadow as well as effective regs
> > should be properly initialized, specifically for a newly created VCPU.
> 
> Could you retry after pushing SET_GUEST_DEBUG at the end of
> kvm_arch_put_registers? Maybe it is no good idea to run get/set_rflags
> without having the sregs properly initialized.
> 
> Jan

Can't reproduce (with the original patch, KVM_SET_GUEST_DEBUG at
beginning of arch_put_regs). Different test box though. Go figure.

Anyway, as you mentioned, the workaround can be made cleaner through
set_vcpu_events.