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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

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



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