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

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Message-ID: <CAB=NE6VVwUYdcfBQRK7bQi3KMrQEOGY=Ar3MdNXp4P7wF192RA@mail.gmail.com>
Date:	Wed, 24 Feb 2016 08:22:10 -0800
From:	"Luis R. Rodriguez" <mcgrof@...nel.org>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	xen-devel <xen-devel@...ts.xenproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [Xen-devel] [PATCH] xen/x86: Zero out .bss for PV guests

On Wed, Feb 24, 2016 at 6:58 AM, David Vrabel <david.vrabel@...rix.com> wrote:
> Yes.  Can you respin with a commit message explaining?  (Or just provide
> the message here and I'll fix it up).

Is there no way to re-use somehow the clear_bss() from bare metal?
This uses a section range:

/* Don't add a printk in there. printk relies on the PDA which is not
initialized
   yet. */
static void __init clear_bss(void)
{
        memset(__bss_start, 0,
               (unsigned long) __bss_stop - (unsigned long) __bss_start);
}

Perhaps the section range might be different for PV guests? Or can
this simply not work even if one added a guest bss section size, or
would it be too late for PV guests, ie we need to do it in asm on PV
guests as you did? If so why.

 Luis