linux-kernel - Re: [PATCH 5.6 096/166] x86/xen: Make the boot CPU idle task reliable

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Date:   Wed, 22 Apr 2020 13:05:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jürgen Groß <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.6 096/166] x86/xen: Make the boot CPU idle task reliable

On Wed, Apr 22, 2020 at 12:45:32PM +0200, Jürgen Groß wrote:
> On 22.04.20 11:57, Greg Kroah-Hartman wrote:
> > From: Miroslav Benes <mbenes@...e.cz>
> > 
> > [ Upstream commit 2f62f36e62daec43aa7b9633ef7f18e042a80bed ]
> > 
> > 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>
> > Signed-off-by: Juergen Gross <jgross@...e.com>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> You'll need upstream d6f34f4c6b4a96 ("x86/xen: fix booting 32-bit pv
> guest"), too.

Thanks for that, now queued up.

greg k-h