linux-kernel - Re: [Xen-devel] [PATCH] xen: p2m: correctly initialize partial p2m leave

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Message-ID: <4D3F1B05.3060008@canonical.com>
Date:	Tue, 25 Jan 2011 19:48:37 +0100
From:	Stefan Bader <stefan.bader@...onical.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen: p2m: correctly initialize partial p2m
 leave

On 01/25/2011 05:54 PM, Ian Campbell wrote:
> Please always include an inline copy of a patch for easier
> review-by-reply, even if you also include an attachment because your
> mailer mangles patches.
> 
Will try to remember. It easy to forget when the mailer used does show textual
attachments inline.

> Anyway, I suspect the following comment is obsoleted by Jeremy's "just
> do it in place" suggestion but:
> 
> On Thu, 2011-01-20 at 14:38 +0000, Stefan Bader wrote:
>> [...]
>> +                       unsigned long **p2m = extend_brk(PAGE_SIZE, PAGE_SIZE);
> 
> I think this would need to be matched by a corresponding RESERVE_BRK of some sort.
> 
> Ian.
> 
> 
Currently the version extending brk is upstream. So we would need this going
upstream as well...

--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -61,6 +61,7 @@ static RESERVE_BRK_ARRAY(unsigned long *, p2m_top_mfn_p, P2M_T

 RESERVE_BRK(p2m_mid, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PE
 RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MI
+RESERVE_BRK(p2m_node, PAGE_SIZE);

 static inline unsigned p2m_top_index(unsigned long pfn)
 {

(code above not tested at all)

And for the "do it inline" this could possibly look like this? (I know I am
repeating myself though the value at max_pfn always seemed to be 3L which seemed
to be too consistent for coincidence)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index ddc81a0..fd12d7c 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -241,21 +241,15 @@ void __init xen_build_dynamic_phys_to_machine(void)
                 * As long as the mfn_list has enough entries to completely
                 * fill a p2m page, pointing into the array is ok. But if
                 * not the entries beyond the last pfn will be undefined.
-                * And guessing that the 'what-ever-there-is' does not take it
-                * too kindly when changing it to invalid markers, a new page
-                * is allocated, initialized and filled with the valid part.
                 */
                if (unlikely(pfn + P2M_PER_PAGE > max_pfn)) {
                        unsigned long p2midx;
-                       unsigned long *p2m = extend_brk(PAGE_SIZE, PAGE_SIZE);
-                       p2m_init(p2m);
-
-                       for (p2midx = 0; pfn + p2midx < max_pfn; p2midx++) {
-                               p2m[p2midx] = mfn_list[pfn + p2midx];
-                       }
-                       p2m_top[topidx][mididx] = p2m;
-               } else
-                       p2m_top[topidx][mididx] = &mfn_list[pfn];
+
+                       p2midx = max_pfn % P2M_PER_PAGE;
+                       for ( ; p2midx < P2M_PER_PAGE; p2midx++)
+                               mfn_list[pfn + p2midx] = INVALID_P2M_ENTRY;
+               }
+               p2m_top[topidx][mididx] = &mfn_list[pfn];
        }

        m2p_override_init();

(again completely (not even compile) tested)

-Stefan
--
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