Hi,
please add the upstream commit 338b522ca43cfd32d11a370f4203bcd089c6c877
("perf/x86/intel: Protect LBR and extra_regs against KVM lying") to
-stable. (mainly 3.14, but it affects any kernel from 3.12 to 3.15)
This commit fixes a kernel crash that happens very reliably inside a Qemu
guest, where the host has Intel CPU, and "-cpu host" is given to the
command line. Relevant stack trace is like the following:
(which was originally reported by my colleage Mohammed Gamal)
====
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.12.26-1-pserver #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88013aa78000 ti: ffff88013aa54000 task.ti: ffff88013aa54000
RIP: 0010:[<ffffffff81ce444d>] [<ffffffff81ce444d>] intel_pmu_init+0x2f1/0x921
RSP: 0000:ffff88013aa55e28 EFLAGS: 00000202
RAX: 0000000000000003 RBX: 0000000000000000 RCX: 0000000000000345
RDX: 0000000000000003 RSI: 0000000000000730 RDI: 0000ffffffffffff
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000007
R10: 0000000000000001 R11: ffffffff81cbb160 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88013fc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88013ffff000 CR3: 0000000001c0b000 CR4: 00000000001406f0
Stack:
ffffffff81cbdd60 ffffffff81ce3437 0000000000000001 ffffffff81ce3466
0000000000000000 ffffffff81cdf291 ffffffff81ce3437 0000000000000001
0000000000000000 0000000000000000 0000000000000000 ffffffff8100021a
Call Trace:
[<ffffffff81ce3437>] ? check_bugs+0x2e/0x2e
[<ffffffff81ce3466>] ? init_hw_perf_events+0x2f/0x4e1
[<ffffffff81cdf291>] ? set_real_mode_permissions+0x93/0x9e
[<ffffffff81ce3437>] ? check_bugs+0x2e/0x2e
[<ffffffff8100021a>] ? do_one_initcall+0x4a/0x170
[<ffffffff8109f46f>] ? clockevents_register_device+0xdf/0x170
[<ffffffff81ce90a9>] ? native_smp_prepare_cpus+0x35d/0x389
[<ffffffff81cdc8a3>] ? kernel_init_freeable+0x95/0x1c6
[<ffffffff81709920>] ? rest_init+0x80/0x80
[<ffffffff81709929>] ? kernel_init+0x9/0xf0
[<ffffffff8171d27c>] ? ret_from_fork+0x7c/0xb0
[<ffffffff81709920>] ? rest_init+0x80/0x80
Code: 6d fd ff 44 89 0d bc 6d fd ff 89 0d 76 6e fd ff 7e
2b 83 e2 1f b8 03 00 00 00 b9 45 03 00 00 83 fa 02 0f 4f c2 89 05 83
6d fd ff <0f> 32 48 c1 e2 20 89 c0 48 09 c2 48 89 15 21 6e fd ff e8 1c 67
RIP [<ffffffff81ce444d>] intel_pmu_init+0x2f1/0x921
RSP <ffff88013aa55e28>
---[ end trace caccfda5c953b0c5 ]---
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
====
I'm already aware that this commit is longer than 100 lines, which is
not ideal for -stable. However, without this commit, a guest kernel
crashes every time. Given that it's actually a serious issue, please
consider taking this patch. I'm not aware of any alternative, such as
a simpler commit to fix the bug.
Sidenote: I also tried to backport this commit to 3.10, but no luck.
3.10 kernel crashes no matter whether this fix is included or not.
Thanks,
Dongsu
====
>From 338b522ca43cfd32d11a370f4203bcd089c6c877 Mon Sep 17 00:00:00 2001
From: Kan Liang <[email protected]>
Date: Mon, 14 Jul 2014 12:25:56 -0700
Subject: [PATCH] perf/x86/intel: Protect LBR and extra_regs against KVM lying
With -cpu host, KVM reports LBR and extra_regs support, if the host has
support.
When the guest perf driver tries to access LBR or extra_regs MSR,
it #GPs all MSR accesses,since KVM doesn't handle LBR and extra_regs support.
So check the related MSRs access right once at initialization time to avoid
the error access at runtime.
For reproducing the issue, please build the kernel with CONFIG_KVM_INTEL = y
(for host kernel).
And CONFIG_PARAVIRT = n and CONFIG_KVM_GUEST = n (for guest kernel).
Start the guest with -cpu host.
Run perf record with --branch-any or --branch-filter in guest to trigger LBR
Run perf stat offcore events (E.g. LLC-loads/LLC-load-misses ...) in guest to
trigger offcore_rsp #GP
Signed-off-by: Kan Liang <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Maria Dimakopoulou <[email protected]>
Cc: Mark Davies <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Yan, Zheng <[email protected]>
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/kernel/cpu/perf_event.c | 3 ++
arch/x86/kernel/cpu/perf_event.h | 12 ++++---
arch/x86/kernel/cpu/perf_event_intel.c | 66 +++++++++++++++++++++++++++++++++-
3 files changed, 75 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 2bdfbff..2879ecd 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -118,6 +118,9 @@ static int x86_pmu_extra_regs(u64 config, struct perf_event
*event)
continue;
if (event->attr.config1 & ~er->valid_mask)
return -EINVAL;
+ /* Check if the extra msrs can be safely accessed*/
+ if (!er->extra_msr_access)
+ return -ENXIO;
reg->idx = er->idx;
reg->config = event->attr.config1;
diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index 3b2f9bd..8ade931 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -295,14 +295,16 @@ struct extra_reg {
u64 config_mask;
u64 valid_mask;
int idx; /* per_xxx->regs[] reg index */
+ bool extra_msr_access;
};
#define EVENT_EXTRA_REG(e, ms, m, vm, i) { \
- .event = (e), \
- .msr = (ms), \
- .config_mask = (m), \
- .valid_mask = (vm), \
- .idx = EXTRA_REG_##i, \
+ .event = (e), \
+ .msr = (ms), \
+ .config_mask = (m), \
+ .valid_mask = (vm), \
+ .idx = EXTRA_REG_##i, \
+ .extra_msr_access = true, \
}
#define INTEL_EVENT_EXTRA_REG(event, msr, vm, idx) \
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c
b/arch/x86/kernel/cpu/perf_event_intel.c
index c206815..2502d0d 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2182,6 +2182,41 @@ static void intel_snb_check_microcode(void)
}
}
+/*
+ * Under certain circumstances, access certain MSR may cause #GP.
+ * The function tests if the input MSR can be safely accessed.
+ */
+static bool check_msr(unsigned long msr, u64 mask)
+{
+ u64 val_old, val_new, val_tmp;
+
+ /*
+ * Read the current value, change it and read it back to see if it
+ * matches, this is needed to detect certain hardware emulators
+ * (qemu/kvm) that don't trap on the MSR access and always return 0s.
+ */
+ if (rdmsrl_safe(msr, &val_old))
+ return false;
+
+ /*
+ * Only change the bits which can be updated by wrmsrl.
+ */
+ val_tmp = val_old ^ mask;
+ if (wrmsrl_safe(msr, val_tmp) ||
+ rdmsrl_safe(msr, &val_new))
+ return false;
+
+ if (val_new != val_tmp)
+ return false;
+
+ /* Here it's sure that the MSR can be safely accessed.
+ * Restore the old value and return.
+ */
+ wrmsrl(msr, val_old);
+
+ return true;
+}
+
static __init void intel_sandybridge_quirk(void)
{
x86_pmu.check_microcode = intel_snb_check_microcode;
@@ -2271,7 +2306,8 @@ __init int intel_pmu_init(void)
union cpuid10_ebx ebx;
struct event_constraint *c;
unsigned int unused;
- int version;
+ struct extra_reg *er;
+ int version, i;
if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
switch (boot_cpu_data.x86) {
@@ -2577,5 +2613,33 @@ __init int intel_pmu_init(void)
}
}
+ /*
+ * Access LBR MSR may cause #GP under certain circumstances.
+ * E.g. KVM doesn't support LBR MSR
+ * Check all LBT MSR here.
+ * Disable LBR access if any LBR MSRs can not be accessed.
+ */
+ if (x86_pmu.lbr_nr && !check_msr(x86_pmu.lbr_tos, 0x3UL))
+ x86_pmu.lbr_nr = 0;
+ for (i = 0; i < x86_pmu.lbr_nr; i++) {
+ if (!(check_msr(x86_pmu.lbr_from + i, 0xffffUL) &&
+ check_msr(x86_pmu.lbr_to + i, 0xffffUL)))
+ x86_pmu.lbr_nr = 0;
+ }
+
+ /*
+ * Access extra MSR may cause #GP under certain circumstances.
+ * E.g. KVM doesn't support offcore event
+ * Check all extra_regs here.
+ */
+ if (x86_pmu.extra_regs) {
+ for (er = x86_pmu.extra_regs; er->msr; er++) {
+ er->extra_msr_access = check_msr(er->msr, 0x1ffUL);
+ /* Disable LBR select mapping */
+ if ((er->idx == EXTRA_REG_LBR) && !er->extra_msr_access)
+ x86_pmu.lbr_sel_map = NULL;
+ }
+ }
+
return 0;
}
--
1.9.3
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