linux-kernel - Re: [PATCH v3 1/2] x86/xen: Make the boot CPU idle task reliable

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Message-ID: <f743b8bd-7552-24a8-e7bc-fa8b3bbcb9d2@suse.com>
Date:   Thu, 26 Mar 2020 10:29:40 +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 1/2] x86/xen: Make the boot CPU idle task reliable

On 26.03.20 10:26, Miroslav Benes wrote:
> The unwinder reports the boot CPU idle task's stack on XEN PV as
> unreliable, which affects at least live patching. There are two reasons
> for this. First, the task does not follow the x86 convention that its
> stack starts at the offset right below saved pt_regs. It allows the
> unwinder to easily detect the end of the stack and verify it. Second,
> startup_xen() function does not store the return address before jumping
> to xen_start_kernel() which confuses the unwinder.
> 
> Amend both issues by moving the starting point of initial stack in
> startup_xen() and storing the return address before the jump, which is
> exactly what call instruction does.
> 
> Signed-off-by: Miroslav Benes <mbenes@...e.cz>

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


Juergen