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

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Message-ID: <56CDC520.1000609@citrix.com>
Date:	Wed, 24 Feb 2016 14:58:40 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Andrew Cooper <andrew.cooper3@...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 24/02/16 14:52, Boris Ostrovsky wrote:
> 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.

Yes.  Can you respin with a commit message explaining?  (Or just provide
the message here and I'll fix it up).

David