From fe651573b718ba19bfd5e68365103f8747c9d9d1 Mon Sep 17 00:00:00 2001 From: Josh Boyer Date: Mon, 12 Jan 2015 08:17:01 -0500 Subject: [PATCH] Add patch to fix loop in VDSO (rhbz 1178975) --- kernel.spec | 9 ++++ x86-vdso-Use-asm-volatile-in-__getcpu.patch | 55 +++++++++++++++++++++ 2 files changed, 64 insertions(+) create mode 100644 x86-vdso-Use-asm-volatile-in-__getcpu.patch diff --git a/kernel.spec b/kernel.spec index a4c08e9b4..84eb6dacb 100644 --- a/kernel.spec +++ b/kernel.spec @@ -614,6 +614,9 @@ Patch26092: xhci-Add-broken-streams-quirk-for-Fresco-Logic-FL100.patch Patch26093: uas-Add-US_FL_NO_ATA_1X-for-Seagate-devices-with-usb.patch Patch26094: uas-Add-US_FL_NO_REPORT_OPCODES-for-JMicron-JMS566-w.patch +#rhbz 1178975 +Patch26125: x86-vdso-Use-asm-volatile-in-__getcpu.patch + # git clone ssh://git.fedorahosted.org/git/kernel-arm64.git, git diff master...devel Patch30000: kernel-arm64.patch @@ -1336,6 +1339,9 @@ ApplyPatch xhci-Add-broken-streams-quirk-for-Fresco-Logic-FL100.patch ApplyPatch uas-Add-US_FL_NO_ATA_1X-for-Seagate-devices-with-usb.patch ApplyPatch uas-Add-US_FL_NO_REPORT_OPCODES-for-JMicron-JMS566-w.patch +#rhbz 1178975 +ApplyPatch x86-vdso-Use-asm-volatile-in-__getcpu.patch + %if 0%{?aarch64patches} ApplyPatch kernel-arm64.patch %ifnarch aarch64 # this is stupid, but i want to notice before secondary koji does. @@ -2202,6 +2208,9 @@ fi # ||----w | # || || %changelog +* Mon Jan 12 2015 Josh Boyer +- Add patch to fix loop in VDSO (rhbz 1178975) + * Fri Jan 09 2015 Josh Boyer - 3.19.0-0.rc3.git2.1 - Linux v3.19-rc3-69-g11c8f01b423b diff --git a/x86-vdso-Use-asm-volatile-in-__getcpu.patch b/x86-vdso-Use-asm-volatile-in-__getcpu.patch new file mode 100644 index 000000000..8cdf8e7c6 --- /dev/null +++ b/x86-vdso-Use-asm-volatile-in-__getcpu.patch @@ -0,0 +1,55 @@ +From 1ddf0b1b11aa8a90cef6706e935fc31c75c406ba Mon Sep 17 00:00:00 2001 +From: Andy Lutomirski +Date: Sun, 21 Dec 2014 08:57:46 -0800 +Subject: x86, vdso: Use asm volatile in __getcpu + +In Linux 3.18 and below, GCC hoists the lsl instructions in the +pvclock code all the way to the beginning of __vdso_clock_gettime, +slowing the non-paravirt case significantly. For unknown reasons, +presumably related to the removal of a branch, the performance issue +is gone as of + +e76b027e6408 x86,vdso: Use LSL unconditionally for vgetcpu + +but I don't trust GCC enough to expect the problem to stay fixed. + +There should be no correctness issue, because the __getcpu calls in +__vdso_vlock_gettime were never necessary in the first place. + +Note to stable maintainers: In 3.18 and below, depending on +configuration, gcc 4.9.2 generates code like this: + + 9c3: 44 0f 03 e8 lsl %ax,%r13d + 9c7: 45 89 eb mov %r13d,%r11d + 9ca: 0f 03 d8 lsl %ax,%ebx + +This patch won't apply as is to any released kernel, but I'll send a +trivial backported version if needed. + +Fixes: 51c19b4f5927 x86: vdso: pvclock gettime support +Cc: stable@vger.kernel.org # 3.8+ +Cc: Marcelo Tosatti +Acked-by: Paolo Bonzini +Signed-off-by: Andy Lutomirski + +diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h +index e7e9682..f556c48 100644 +--- a/arch/x86/include/asm/vgtod.h ++++ b/arch/x86/include/asm/vgtod.h +@@ -80,9 +80,11 @@ static inline unsigned int __getcpu(void) + + /* + * Load per CPU data from GDT. LSL is faster than RDTSCP and +- * works on all CPUs. ++ * works on all CPUs. This is volatile so that it orders ++ * correctly wrt barrier() and to keep gcc from cleverly ++ * hoisting it out of the calling function. + */ +- asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG)); ++ asm volatile ("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG)); + + return p; + } +-- +cgit v0.10.2 +