linux-kernel - Re: [PATCH v3 2/2] x86/xen: Make the secondary CPU idle tasks reliable

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Date:   Thu, 26 Mar 2020 10:30:09 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Miroslav Benes <mbenes@...e.cz>, boris.ostrovsky@...cle.com,
        sstabellini@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, jpoimboe@...hat.com
Cc:     x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        jslaby@...e.cz, andrew.cooper3@...rix.com, jbeulich@...e.com
Subject: Re: [PATCH v3 2/2] x86/xen: Make the secondary CPU idle tasks
 reliable

On 26.03.20 10:26, Miroslav Benes wrote:
> The unwinder reports the secondary CPU idle tasks' stack on XEN PV as
> unreliable, which affects at least live patching.
> cpu_initialize_context() sets up the context of the CPU through
> VCPUOP_initialise hypercall. After it is woken up, the idle task starts
> in cpu_bringup_and_idle() function and its stack starts at the offset
> right below pt_regs. The unwinder correctly detects the end of stack
> there but it is confused by NULL return address in the last frame.
> 
> Introduce a wrapper in assembly, which just calls
> cpu_bringup_and_idle(). The return address is thus pushed on the stack
> and the wrapper contains the annotation hint for the unwinder regarding
> the stack state.
> 
> Signed-off-by: Miroslav Benes <mbenes@...e.cz>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen