linux-kernel - Re: [Xen-devel] [PATCH] xen/x86: Zero out .bss for PV guests

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Message-ID: <56CDC39B.3060004@oracle.com>
Date:	Wed, 24 Feb 2016 09:52:11 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Andrew Cooper <andrew.cooper3@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>, konrad.wilk@...cle.com
Cc:	xen-devel@...ts.xenproject.org, mcgrof@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] xen/x86: Zero out .bss for PV guests

On 02/24/2016 09:15 AM, Andrew Cooper wrote:
> On 24/02/16 14:12, David Vrabel wrote:
>> On 22/02/16 22:06, Boris Ostrovsky wrote:
>>> Baremetal kernels clear .bss early in the boot. Since Xen PV guests don't
>>> excecute that early code they should do it too.
>>>
>>> (Since we introduce macros for specifying 32- and 64-bit registers we
>>> can get rid of ifdefs in startup_xen())
>> .bss must have been cleared for PV guests otherwise they would be
>> horribly broken.  What was the method and why is it no longer sufficient?

I couldn't find this being done anywhere, hence this patch.

> The domain builder hands out zeroed pages.  I don't believe we guarantee
> that the guests RAM is clean, but it is in practice.

OK, that's what I suspected but didn't actually look.

I, in fact, wonder whether this should go to stable trees as well.

-boris