[PATCH 4.6 26/56] x86/mtrr: Fix Xorg crashes in Qemu sessions

From	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Newsgroups	linux.kernel
Subject	[PATCH 4.6 26/56] x86/mtrr: Fix Xorg crashes in Qemu sessions
Date	2016-08-14 23:00 +0200
Message-ID	<s6aFI-4Et-29@gated-at.bofh.it> (permalink)
References	<s6amm-4wI-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Toshi Kani <toshi.kani@hpe.com>

commit edfe63ec97ed8d4496225f7ba54c9ce4207c5431 upstream.

A Xorg failure on qemu32 was reported as a regression [1] caused by
commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled").

This patch fixes the Xorg crash.

Negative effects of this regression were the following two failures [2]
in Xorg on QEMU with QEMU CPU model "qemu32" (-cpu qemu32), which were
triggered by the fact that its virtual CPU does not support MTRRs.

 #1. copy_process() failed in the check in reserve_pfn_range()

    copy_process
     copy_mm
      dup_mm
       dup_mmap
        copy_page_range
         track_pfn_copy
          reserve_pfn_range

 A WC map request was tracked as WC in memtype, which set a PTE as
 UC (pgprot) per __cachemode2pte_tbl[].  This led to this error in
 reserve_pfn_range() called from track_pfn_copy(), which obtained
 a pgprot from a PTE.  It converts pgprot to page_cache_mode, which
 does not necessarily result in the original page_cache_mode since
 __cachemode2pte_tbl[] redirects multiple types to UC.

 #2. error path in copy_process() then hit WARN_ON_ONCE in
     untrack_pfn().

     x86/PAT: Xorg:509 map pfn expected mapping type uncached-
     minus for [mem 0xfd000000-0xfdffffff], got write-combining
      Call Trace:
     dump_stack
     warn_slowpath_common
     ? untrack_pfn
     ? untrack_pfn
     warn_slowpath_null
     untrack_pfn
     ? __kunmap_atomic
     unmap_single_vma
     ? pagevec_move_tail_fn
     unmap_vmas
     exit_mmap
     mmput
     copy_process.part.47
     _do_fork
     SyS_clone
     do_syscall_32_irqs_on
     entry_INT80_32

These negative effects are caused by two separate bugs, but they
can be addressed in separate patches.  Fixing the pat_init() issue
described below addresses the root cause, and avoids Xorg to hit
these cases.

When the CPU does not support MTRRs, MTRR does not call pat_init(),
which leaves PAT enabled without initializing PAT.  This pat_init()
issue is a long-standing issue, but manifested as issue #1 (and then
hit issue #2) with the above-mentioned commit because the memtype
now tracks cache attribute with 'page_cache_mode'.

This pat_init() issue existed before the commit, but we used pgprot
in memtype.  Hence, we did not have issue #1 before.  But WC request
resulted in WT in effect because WC pgrot is actually WT when PAT
is not initialized.  This is not how it was designed to work.  When
PAT is set to disable properly, WC is converted to UC.  The use of
WT can result in a system crash if the target range does not support
WT.  Fortunately, nobody ran into such issue before.

To fix this pat_init() issue, PAT code has been enhanced to provide
pat_disable() interface.  Call this interface when MTRRs are disabled.
By setting PAT to disable properly, PAT bypasses the memtype check,
and avoids issue #1.

  [1]: https://lkml.org/lkml/2016/3/3/828
  [2]: https://lkml.org/lkml/2016/3/4/775

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: elliott@hpe.com
Cc: konrad.wilk@oracle.com
Cc: paul.gortmaker@windriver.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1458769323-24491-5-git-send-email-toshi.kani@hpe.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/include/asm/mtrr.h     |    6 +++++-
 arch/x86/kernel/cpu/mtrr/main.c |   10 +++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/mtrr.h
+++ b/arch/x86/include/asm/mtrr.h
@@ -24,6 +24,7 @@
 #define _ASM_X86_MTRR_H
 
 #include <uapi/asm/mtrr.h>
+#include <asm/pat.h>
 
 
 /*
@@ -83,9 +84,12 @@ static inline int mtrr_trim_uncached_mem
 static inline void mtrr_centaur_report_mcr(int mcr, u32 lo, u32 hi)
 {
 }
+static inline void mtrr_bp_init(void)
+{
+	pat_disable("MTRRs disabled, skipping PAT initialization too.");
+}
 
 #define mtrr_ap_init() do {} while (0)
-#define mtrr_bp_init() do {} while (0)
 #define set_mtrr_aps_delayed_init() do {} while (0)
 #define mtrr_aps_init() do {} while (0)
 #define mtrr_bp_restore() do {} while (0)
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -759,8 +759,16 @@ void __init mtrr_bp_init(void)
 		}
 	}
 
-	if (!mtrr_enabled())
+	if (!mtrr_enabled()) {
 		pr_info("MTRR: Disabled\n");
+
+		/*
+		 * PAT initialization relies on MTRR's rendezvous handler.
+		 * Skip PAT init until the handler can initialize both
+		 * features independently.
+		 */
+		pat_disable("MTRRs disabled, skipping PAT initialization too.");
+	}
 }
 
 void mtrr_ap_init(void)

Thread

[PATCH 4.6 00/56] 4.6.7-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:40 +0200
  [PATCH 4.6 56/56] ext4: fix reference counting bug on block allocation error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 02/56] libnvdimm, pfn, dax: fix initialization vs autodetect for mode + alignment Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 28/56] x86/xen, pat: Remove PAT table init code from Xen Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 35/56] mm: memcontrol: fix memcg id ref counter on swap charge move Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 06/56] bonding: set carrier off for devices created through netlink Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 34/56] mm: memcontrol: fix swap counter leak on swapout from offline cgroup Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 32/56] powerpc/eeh: Fix invalid cached PE primary bus Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 39/56] radix-tree: account nodes to memcg only if explicitly requested Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 45/56] Revert "mm, mempool: only set __GFP_NOMEMALLOC if there are free elements" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 41/56] x86/power/64: Fix hibernation return address corruption Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 22/56] random: strengthen input validation for RNDADDTOENTCNT Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 54/56] ext4: validate s_reserved_gdt_blocks on mount Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 37/56] block: fix use-after-free in seq file Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 51/56] ext4: check for extents that wrap around Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 27/56] x86/mtrr: Fix PAT init handling when MTRR is disabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 05/56] tcp: enable per-socket rate limiting of all challenge acks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 25/56] x86/mm/pat: Replace cpu_has_pat with boot_cpu_has() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 21/56] regulator: qcom_smd: Remove list_voltage callback for rpm_smps_ldo_ops_fixed Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 47/56] Revert "cpufreq: pcc-cpufreq: update default value of cpuinfo_transition_latency" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 50/56] serial: mvebu-uart: free the IRQ in ->shutdown() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 53/56] ext4: dont call ext4_should_journal_data() on the journal inode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 46/56] fs/dcache.c: avoid soft-lockup in dput() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 48/56] crypto: gcm - Filter out async ghash if necessary Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 09/56] bridge: Fix incorrect re-injection of LLDP packets Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 30/56] x86/mm/pat: Fix BUG_ON() in mmap_mem() on QEMU/i386 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 38/56] sysv, ipc: fix security-layer leaking Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 44/56] fuse: fix wrong assignment of ->flags in fuse_send_init() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 18/56] IB/hfi1: Correct issues with sc5 computation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 16/56] arm: oabi compat: add missing access checks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 17/56] KEYS: 64-bit MIPS needs to use compat_sys_keyctl for 32-bit userspace Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:50 +0200
  [PATCH 4.6 42/56] fuse: fsync() did not return IO errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 36/56] x86/syscalls/64: Add compat_sys_keyctl for 32-bit userspace Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 29/56] x86/pat: Document the PAT initialization sequence Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 40/56] x86/microcode: Fix suspend to RAM with builtin microcode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 33/56] powerpc/bpf/jit: Disable classic BPF JIT on ppc64le Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 26/56] x86/mtrr: Fix Xorg crashes in Qemu sessions Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 23/56] x86/mm/pat: Add support of non-default PAT MSR setting Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 52/56] ext4: fix deadlock during page writeback Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 55/56] ext4: short-cut orphan cleanup on error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 31/56] udf: Prevent stack overflow on corrupted filesystem mount Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 43/56] fuse: fuse_flush must check mapping->flags for errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 49/56] crypto: scatterwalk - Fix test in scatterwalk_done Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:00 +0200
  [PATCH 4.6 20/56] apparmor: fix ref count leak when profile sha1 hash is read Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:10 +0200
  [PATCH 4.6 04/56] tcp: make challenge acks less predictable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:10 +0200
  [PATCH 4.6 03/56] ppp: defer netns reference release for ppp channel Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:10 +0200
  [PATCH 4.6 19/56] IB/hfi1: Fix deadlock with txreq allocation slow path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:10 +0200
  [PATCH 4.6 08/56] vlan: use a valid default mtu value for vlan over macsec Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:10 +0200
  [PATCH 4.6 07/56] net: bgmac: Fix infinite loop in bgmac_dma_tx_add() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:10 +0200
  [PATCH 4.6 24/56] x86/mm/pat: Add pat_disable() interface Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 23:10 +0200
  Re: [PATCH 4.6 00/56] 4.6.7-stable review Guenter Roeck <linux@roeck-us.net> - 2016-08-15 15:10 +0200
  Re: [PATCH 4.6 00/56] 4.6.7-stable review Shuah Khan <shuah.kh@samsung.com> - 2016-08-16 06:10 +0200

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