Re: [Xen-devel] current not very current (vs curr_vcpu)

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Sat, 20 Feb 2010 07:45:26 +0000
Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:

> On 20/02/2010 03:50, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:
> 
> > ah, I see what's going on. context_switch() is scheduling idle
> > vcpu, and calls continue_idle_domain() to
> > reset_stack_and_jump(idle_loop). well, reset_stack_and_jump() is
> > setting rsp to guest_cpu_user_regs(), and interrupt is coming right
> > at that instant. so:
> > 
> > diff = (char *)guest_cpu_user_regs() - (char *)(r)  is 0
> > 
> > and as a result, guest_mode(regs) == true.
> 
> Well, I don't see how this scenario works. If rsp==g_c_u_r() at the
> instant the interrupt comes in, then the stack frame for the
> interrupt will be *above* g_c_u_r(). Thus 'diff' in guest_mode() will
> evaluate non-zero and positive, and regs->{rip,rsp} should point at
> hypervisor code/stack.
> 
> Also: in your original email you said regs.rsp pointed at dom0 stack.
> That doesn't tally with you saying that rsp==g_c_u_r() (an address in
> hypervisor space) immediately before the interrupt, in this email.
> Regs->rsp in the scenario you describe here should be exactly equal
> to g_c_u_r().
> 
>  -- Keir
> 

yes, you are right! Interrupt coming in would make rsp go up, 
my brain missed it. regs->rsp and rip clearly indicate cpu in
dom0, I thought friday that may be it was showing stale entries. I'll
continue debugging more, instrumented hypervisor seems to indicate
interrupt coming in during context switch, but I need to
fine grain it. Will keep you posted.

thanks,
Mukesh

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