Patch "mm: don't defer struct page initialization for Xen pv guests" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

mm: don't defer struct page initialization for Xen pv guests

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-don-t-defer-struct-page-initialization-for-xen-pv-guests.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Juergen Gross <[email protected]>
Date: Wed, 21 Feb 2018 14:46:09 -0800
Subject: mm: don't defer struct page initialization for Xen pv guests

From: Juergen Gross <[email protected]>

commit 895f7b8e90200cf1a5dc313329369adf30e51f9a upstream.

Commit f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap") broke Xen pv domains in some configurations, as the "Pinned" information in struct page of early page tables could get lost.

This will lead to the kernel trying to write directly into the page tables instead of asking the hypervisor to do so. The result is a crash like the following:

  BUG: unable to handle kernel paging request at ffff8801ead19008
  IP: xen_set_pud+0x4e/0xd0
  PGD 1c0a067 P4D 1c0a067 PUD 23a0067 PMD 1e9de0067 PTE 80100001ead19065
  Oops: 0003 [#1] PREEMPT SMP
  Modules linked in:
  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-default+ #271
  Hardware name: Dell Inc. Latitude E6440/0159N7, BIOS A07 06/26/2014
  task: ffffffff81c10480 task.stack: ffffffff81c00000
  RIP: e030:xen_set_pud+0x4e/0xd0
  Call Trace:
   __pmd_alloc+0x128/0x140
   ioremap_page_range+0x3f4/0x410
   __ioremap_caller+0x1c3/0x2e0
   acpi_os_map_iomem+0x175/0x1b0
   acpi_tb_acquire_table+0x39/0x66
   acpi_tb_validate_table+0x44/0x7c
   acpi_tb_verify_temp_table+0x45/0x304
   acpi_reallocate_root_table+0x12d/0x141
   acpi_early_init+0x4d/0x10a
   start_kernel+0x3eb/0x4a1
   xen_start_kernel+0x528/0x532
  Code: 48 01 e8 48 0f 42 15 a2 fd be 00 48 01 d0 48 ba 00 00 00 00 00 ea ff ff 48 c1 e8 0c 48 c1 e0 06 48 01 d0 48 8b 00 f6 c4 02 75 5d <4c> 89 65 00 5b 5d 41 5c c3 65 8b 05 52 9f fe 7e 89 c0 48 0f a3
  RIP: xen_set_pud+0x4e/0xd0 RSP: ffffffff81c03cd8
  CR2: ffff8801ead19008
  ---[ end trace 38eca2e56f1b642e ]---

Avoid this problem by not deferring struct page initialization when running as Xen pv guest.

Pavel said:

: This is unique for Xen, so this particular issue won't effect other : configurations. I am going to investigate if there is a way to : re-enable deferred page initialization on xen guests.

---
 mm/page_alloc.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -46,6 +46,7 @@
 #include <linux/stop_machine.h>
 #include <linux/sort.h>
 #include <linux/pfn.h>
+#include <xen/xen.h>
 #include <linux/backing-dev.h>
 #include <linux/fault-inject.h>
 #include <linux/page-isolation.h>

@@ -347,6 +348,9 @@ static inline bool update_defer_init(pg_
 	/* Always populate low zones for address-contrained allocations */
 	if (zone_end < pgdat_end_pfn(pgdat))
 		return true;
+	/* Xen PV domains need page structures early */
+	if (xen_pv_domain())
+		return true;
 	(*nr_initialised)++;
 	if ((*nr_initialised > pgdat->static_init_pgcnt) &&
 	    (pfn & (PAGES_PER_SECTION - 1)) == 0) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/mm-don-t-defer-struct-page-initialization-for-xen-pv-guests.patch queue-4.15/mm-swap-frontswap-fix-thp-swap-if-frontswap-enabled.patch