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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 19/02/2010 04:21, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:

> I noticed while debugging something that current is not pointing to the
> current vcpu upon serial interrupt. The regs->SP clearly shows 64bit dom0
> stack, guest_mode(regs) returns 1, but current is pointing
> to idle vcpu. I'm not able to figure how this is possible. I can come up
> with scenario where dom0.vcpu yields cpu to idle vcpu in which case
> curr_vcpu will point to dom0.vcpu and current to idle vcpu. But in that
> case guest_mode(regs) will be false, and regs.SP will show hyp stack.
> Correct?
> 
> Am I correct that if guest_mode() then current should always point to
> guest vcpu? If yes, then I will debug this further.

The behaviour you see is expected. Guest_mode() is meaningless when running
an idle vcpu. This is because the guest regs at the bottom of the stack are
junk for an idle vcpu (and also we do lazy state synchronisation, so they
may be the valid active regs for the last scheduled non-idle vcpu).

 -- Keir



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