From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [RFC PATCH 0/2] x86: fix Xen PV regression caused
 by	NUMA page migration
Date: Wed, 26 Mar 2014 19:10:23 +0000
Message-ID: <5333261F.8010004@citrix.com>
References: <1395425902-29817-1-git-send-email-david.vrabel@citrix.com>
Mime-Version: 1.0
Content-Type: multipart/mixed; boundary="------------020607060701080201000703"
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta14.messagelabs.com ([193.109.254.103])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <david.vrabel@citrix.com>) id 1WStDY-0001lp-IP
	for xen-devel@lists.xenproject.org; Wed, 26 Mar 2014 19:10:28 +0000
In-Reply-To: <1395425902-29817-1-git-send-email-david.vrabel@citrix.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: David Vrabel <david.vrabel@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>, xen-devel@lists.xenproject.org, Steven Noonan <steven@uplinklabs.net>, Mel Gorman <mgorman@suse.de>, Elena Ufimtseva <ufimtseva@gmail.com>
List-Id: xen-devel@lists.xenproject.org

--------------020607060701080201000703
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit

On 21/03/14 18:18, David Vrabel wrote:
> This series should properly fix the Xen PV guest regression introduced
> by 1667918b6483 (mm: numa: clear numa hinting information on
> mprotect).  The previous fix a9c8e4beeeb6 (xen: properly account for
> _PAGE_NUMA during xen pte translations) breaks save/restore
> (migration) and needs to be reverted.
> 
> I've only given this series a minimal amount of testing and would
> appreciate testing by someone who experienced/reproduced the original
> regression.

Attached is a simple test program that triggers the bug.

Patch #2 fixes the regression and I think that it is the correct fix but
I need to confirm it doesn't cause any measurable performance problems
on native x86 (I think it should not).

I don't have any more time to work on this until next week.

David

--------------020607060701080201000703
Content-Type: text/x-csrc; name="mprotect.c"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="mprotect.c"

#include <sys/mman.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define PAGE_SIZE 4096
#define MAGIC 0x79128347ul

int main(void)
{
    void *p;
    volatile unsigned long *m;
    int ret;

    /* Map a frame for the test. */
    m = p = mmap(NULL, PAGE_SIZE, PROT_WRITE|PROT_READ, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
    if (p == MAP_FAILED) {
        perror("mmap");
        exit(1);
    }

    /* Write to the frame. */
    *m = MAGIC;

    /* Set PROT_NONE on the mapping. */
    ret = mprotect(p, PAGE_SIZE, PROT_NONE);
    if (ret < 0) {
        perror("mprotect");
        exit(1);
    }

    /*
     * Set PROT_READ (or any other non-PROT_NONE protection) on the
     * mapping.
     *
     * On a buggy system pte_mknonnuma() will clear _PAGE_PROTNONE (==
     * _PAGE_NUMA) and set _PAGE_PRESENT /without/ doing a PFN to MFN
     * conversion.
     *
     * The resulting mapping will be to the wrong MFN.
     */
    ret = mprotect(p, PAGE_SIZE, PROT_READ);
    if (ret < 0) {
        perror("mprotect");
        exit(1);
    }

    /* Check we're still mapping the original frame. */
    if (*m != MAGIC) {
        printf("FAIL (0x%lx != 0x%lx)\n", *m, MAGIC);
        ret = 1;
    }

    /*
     * On a buggy system, the munmap() will usually trigger a "Bad
     * page" error since the mapping isn't for the original page.
     */
    munmap(p, PAGE_SIZE);

    return ret;
}

--------------020607060701080201000703
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel

--------------020607060701080201000703--