* [PATCH]: Make linux smarter about using batched PTE updates
@ 2008-03-11 21:07 Chris Lalancette
2008-03-11 21:17 ` Keir Fraser
0 siblings, 1 reply; 3+ messages in thread
From: Chris Lalancette @ 2008-03-11 21:07 UTC (permalink / raw)
To: xen-devel
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All,
Attached is a patch to make batched PTE updates smarter. Basically, if you
run a kernel with batched PTE capability on a hypervisor that doesn't support
it, you get lots of:
(XEN) mm.c:2453:d2 Invalid page update command 2
(XEN) printk: 333 messages suppressed.
(XEN) mm.c:2453:d2 Invalid page update command 2
on the hypervisor console.
It doesn't seem to be a security problem, since it is rate-limited, but it is an
annoyance. The patch just looks at the return code from the first such
hypercall, and if we fail with ENOSYS, we just mark it as
"hypervisor_no_batch_update" and never try again. Patch originally from Rik van
Riel.
Signed-off-by: Chris Lalancette <clalance@redhat.com>
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[-- Type: text/x-patch, Size: 2332 bytes --]
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Date: Tue, 11 Mar 2008 16:31:08 -0400
From: Rik van Riel <riel@redhat.com>
To: clalance@redhat.com
Subject: quiet down xen mprotect printks
Message-ID: <20080311163108.0d6ae553@cuia.boston.redhat.com>
Organization: Red Hat, Inc
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It doesn't get much simpler than this :)
Please double-check the bit in mm/mmap.c to make sure I did this the right way around.
--- linux-2.6.18.noarch/arch/i386/mm/hypervisor.c.printk 2008-03-11 18:12:34.000000000 -0400
+++ linux-2.6.18.noarch/arch/i386/mm/hypervisor.c 2008-03-11 18:16:38.000000000 -0400
@@ -458,6 +458,7 @@
#endif
#define MAX_BATCHED_FULL_PTES 32
+static int hypervisor_no_batch_update;
int xen_change_pte_range(struct mm_struct *mm, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot)
@@ -467,6 +468,9 @@
pte_t *pte;
spinlock_t *ptl;
+ if (hypervisor_no_batch_update)
+ return 0;
+
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
do {
if (pte_present(*pte)) {
@@ -484,5 +488,8 @@
rc = HYPERVISOR_mmu_update( &u[0], i, NULL, DOMID_SELF);
pte_unmap_unlock(pte - 1, ptl);
BUG_ON(rc && rc != -ENOSYS);
+ /* Don't try again. This hypervisor does not support batch updates. */
+ if (rc == -ENOSYS)
+ hypervisor_no_batch_update = 1;
return !rc;
}
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH]: Make linux smarter about using batched PTE updates
2008-03-11 21:07 [PATCH]: Make linux smarter about using batched PTE updates Chris Lalancette
@ 2008-03-11 21:17 ` Keir Fraser
2008-03-11 21:34 ` Chris Lalancette
0 siblings, 1 reply; 3+ messages in thread
From: Keir Fraser @ 2008-03-11 21:17 UTC (permalink / raw)
To: Chris Lalancette, xen-devel
We expose feature flag XENFEAT_mmu_pt_update_preserve_ad for this purpose,
which means you do not need to attempt the hypercall even once. See
http://xenbits.xensource.com/linux-2.6.18-xen.hg for example usage, in the
very file and function you patch below.
-- Keir
On 11/3/08 21:07, "Chris Lalancette" <clalance@redhat.com> wrote:
> All,
> Attached is a patch to make batched PTE updates smarter. Basically, if
> you
> run a kernel with batched PTE capability on a hypervisor that doesn't support
> it, you get lots of:
>
> (XEN) mm.c:2453:d2 Invalid page update command 2
> (XEN) printk: 333 messages suppressed.
> (XEN) mm.c:2453:d2 Invalid page update command 2
>
> on the hypervisor console.
>
> It doesn't seem to be a security problem, since it is rate-limited, but it is
> an
> annoyance. The patch just looks at the return code from the first such
> hypercall, and if we fail with ENOSYS, we just mark it as
> "hypervisor_no_batch_update" and never try again. Patch originally from Rik
> van
> Riel.
>
> Signed-off-by: Chris Lalancette <clalance@redhat.com>
> Return-Path: <riel@redhat.com>
> Received: from pobox.corp.redhat.com ([unix socket])
> by pobox.corp.redhat.com (Cyrus v2.2.12-Invoca-RPM-2.2.12-8.1.RHEL4) with
> LMTPA;
> Tue, 11 Mar 2008 16:31:11 -0400
> X-Sieve: CMU Sieve 2.2
> Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com
> [172.16.52.254])
> by pobox.corp.redhat.com (8.13.1/8.13.1) with ESMTP id m2BKVBZT029794
> for <clalance@pobox.corp.redhat.com>; Tue, 11 Mar 2008 16:31:11 -0400
> Received: from mail.boston.redhat.com (mail.boston.redhat.com [172.16.76.12])
> by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id m2BKV9K4008734
> for <clalance@int-mx1.corp.redhat.com>; Tue, 11 Mar 2008 16:31:09 -0400
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> by mail.boston.redhat.com (8.13.1/8.13.1) with ESMTP id m2BKV94q020893
> for <clalance@redhat.com>; Tue, 11 Mar 2008 16:31:09 -0400
> Date: Tue, 11 Mar 2008 16:31:08 -0400
> From: Rik van Riel <riel@redhat.com>
> To: clalance@redhat.com
> Subject: quiet down xen mprotect printks
> Message-ID: <20080311163108.0d6ae553@cuia.boston.redhat.com>
> Organization: Red Hat, Inc
> X-Mailer: Claws Mail 3.1.0 (GTK+ 2.12.1; i386-redhat-linux-gnu)
> Mime-Version: 1.0
> Content-Type: text/plain; charset=US-ASCII
> Content-Transfer-Encoding: 7bit
> X-Scanned-By: MIMEDefang 2.58 on 172.16.52.254
>
> It doesn't get much simpler than this :)
>
> Please double-check the bit in mm/mmap.c to make sure I did this the right way
> around.
>
> --- linux-2.6.18.noarch/arch/i386/mm/hypervisor.c.printk 2008-03-11
> 18:12:34.000000000 -0400
> +++ linux-2.6.18.noarch/arch/i386/mm/hypervisor.c 2008-03-11
> 18:16:38.000000000 -0400
> @@ -458,6 +458,7 @@
> #endif
>
> #define MAX_BATCHED_FULL_PTES 32
> +static int hypervisor_no_batch_update;
>
> int xen_change_pte_range(struct mm_struct *mm, pmd_t *pmd,
> unsigned long addr, unsigned long end, pgprot_t newprot)
> @@ -467,6 +468,9 @@
> pte_t *pte;
> spinlock_t *ptl;
>
> + if (hypervisor_no_batch_update)
> + return 0;
> +
> pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
> do {
> if (pte_present(*pte)) {
> @@ -484,5 +488,8 @@
> rc = HYPERVISOR_mmu_update( &u[0], i, NULL, DOMID_SELF);
> pte_unmap_unlock(pte - 1, ptl);
> BUG_ON(rc && rc != -ENOSYS);
> + /* Don't try again. This hypervisor does not support batch updates. */
> + if (rc == -ENOSYS)
> + hypervisor_no_batch_update = 1;
> return !rc;
> }
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2008-03-11 21:34 UTC | newest]
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2008-03-11 21:07 [PATCH]: Make linux smarter about using batched PTE updates Chris Lalancette
2008-03-11 21:17 ` Keir Fraser
2008-03-11 21:34 ` Chris Lalancette
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