[PATCH 3.16.y-ckt 019/126] x86/cpu: Fix SMAP check in PVOPS environments

From	Luis Henriques <luis.henriques@canonical.com>
Newsgroups	linux.kernel
Subject	[PATCH 3.16.y-ckt 019/126] x86/cpu: Fix SMAP check in PVOPS environments
Date	2016-01-06 12:20 +0100
Message-ID	<qNUif-nA-51@gated-at.bofh.it> (permalink)
References	<qNTFw-8jf-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

3.16.7-ckt22 -stable review patch.  If anyone has any objections, please let me know.

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

From: Andrew Cooper <andrew.cooper3@citrix.com>

commit 581b7f158fe0383b492acd1ce3fb4e99d4e57808 upstream.

There appears to be no formal statement of what pv_irq_ops.save_fl() is
supposed to return precisely.  Native returns the full flags, while lguest and
Xen only return the Interrupt Flag, and both have comments by the
implementations stating that only the Interrupt Flag is looked at.  This may
have been true when initially implemented, but no longer is.

To make matters worse, the Xen PVOP leaves the upper bits undefined, making
the BUG_ON() undefined behaviour.  Experimentally, this now trips for 32bit PV
guests on Broadwell hardware.  The BUG_ON() is consistent for an individual
build, but not consistent for all builds.  It has also been a sitting timebomb
since SMAP support was introduced.

Use native_save_fl() instead, which will obtain an accurate view of the AC
flag.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Tested-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: <lguest@lists.ozlabs.org>
Cc: Xen-devel <xen-devel@lists.xen.org>
Link: http://lkml.kernel.org/r/1433323874-6927-1-git-send-email-andrew.cooper3@citrix.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 arch/x86/kernel/cpu/common.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 8fc57acf86f4..3b12b4d1a560 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -282,10 +282,9 @@ __setup("nosmap", setup_disable_smap);
 
 static __always_inline void setup_smap(struct cpuinfo_x86 *c)
 {
-	unsigned long eflags;
+	unsigned long eflags = native_save_fl();
 
 	/* This should have been cleared long ago */
-	raw_local_save_flags(eflags);
 	BUG_ON(eflags & X86_EFLAGS_AC);
 
 	if (cpu_has(c, X86_FEATURE_SMAP)) {
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Thread

[3.16.y-ckt stable] Linux 3.16.7-ckt22 stable review Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 009/126] USB: serial: option: add support for Novatel MiFi USB620L Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 015/126] usb: dwc3: gadget: let us set lower max_speed Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 007/126] drm/i915: quirk backlight present on Macbook 4, 1 Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 032/126] sctp: translate host order to network order when setting a hmacid Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 001/126] iio: lpc32xx_adc: fix warnings caused by enabling unprepared clock Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 038/126] unix: avoid use-after-free in ep_remove_wait_queue Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 034/126] usb: musb: core: fix order of arguments to ulpi write callback Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 027/126] mmc: remove bondage between REQ_META and reliable write Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 006/126] iio: adc: xilinx: Fix VREFN scale Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 035/126] FS-Cache: Add missing initialization of ret in cachefiles_write_page() Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 013/126] USB: qcserial: Fix support for HP lt4112 LTE/HSPA+ Gobi 4G Modem Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 004/126] iio:ad7793: Fix ad7785 product ID Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 023/126] fat: fix fake_offset handling on error path Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 019/126] x86/cpu: Fix SMAP check in PVOPS environments Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 003/126] iio: ad5064: Fix ad5629/ad5669 shift Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 010/126] USB: ti_usb_3410_5052: Add Honeywell HGI80 ID Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 016/126] usb: chipidea: debug: disable usb irq while role switch Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 029/126] packet: do skb_probe_transport_header when we actually have data Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 030/126] packet: only allow extra vlan len on ethernet devices Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 018/126] xhci: Fix a race in usb2 LPM resume, blocking U3 for usb2 devices Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 005/126] x86/fpu: Fix 32-bit signal frame handling Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 011/126] drm/i915: get runtime PM reference around GEM set_caching IOCTL Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 020/126] arm64: restore bogomips information in /proc/cpuinfo Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:20 +0100
  [PATCH 3.16.y-ckt 002/126] iio:ad5064: Make sure ad5064_i2c_write() returns 0 on success Luis Henriques <luis.henriques@canonical.com> - 2016-01-06 12:30 +0100

csiph-web