On Sun, Oct 18, 2015 at 04:20:07PM +0200, Borislav Petkov wrote:
> Ok,
>
> let's try this and see where it takes us. Patch has been only lightly
> tested in kvm - I'll hammer on it for real once we agree about the
> general form.
>
> Aanyway, this patch is something Peter and I have been talking about on
> IRC a couple of times already. I finally found some free time to poke at
> it, here's the result.
>
> Thoughts?
>
> ---
>
> Kill "notsc" cmdline option and all the glue around it. The two boxes
> worldwide which don't have a TSC should disable X86_TSC. Thus, make
> native_sched_clock() use TSC unconditionally, even if the TSC is
> unstable because that's fine there. This gets rid of the static key
> too and makes the function even simpler and faster, which is a Good
> Thing(tm).
>
> The jiffies-fallback is for the !X86_TSC case.
>
> Signed-off-by: Borislav Petkov <b...@suse.de>
> ---
> Documentation/kernel-parameters.txt | 2 -
> Documentation/x86/x86_64/boot-options.txt | 5 ---
> arch/x86/include/asm/tsc.h | 3 +-
> arch/x86/kernel/apic/apic.c | 2 +-
> arch/x86/kernel/tsc.c | 74
> ++++++++-----------------------
> 5 files changed, 21 insertions(+), 65 deletions(-)
...
> +#ifdef CONFIG_X86_TSC
> + /* return the value in ns */
> + return cycles_2_ns(rdtsc());
> +#else
Ok, we have a problem here:
See the splat below. On the init path
start_kernel
|-> sched_init
|-> init_idle
we're calling sched_clock() which does the cycles_2_ns() thing.
However, that cycles_2_ns() thing gets called only in tsc_init() which
comes later in start_kernel().
Which means, data in this line
ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, data->cyc2ns_shift);
is NULL.
Now, the question is, can I push only the cyc2ns_init() call up, before
sched_init()?
I mean, it dummy initializes only the per-cpu variable and tsc_init()
will correct it anyway, as the comment says:
/*
* Secondary CPUs do not run through tsc_init(), so set up
* all the scale factors for all CPUs, assuming the same
* speed as the bootup CPU. (cpufreq notifiers will fix this
* up if their speed diverges)
*/
for_each_possible_cpu(cpu) {
cyc2ns_init(cpu);
set_cyc2ns_scale(cpu_khz, cpu);
}
Thoughts?
[ 0.000000] BUG: unable to handle kernel NULL pointer dereference at
(null)
[ 0.000000] IP: [<ffffffff8100d19d>] native_sched_clock+0x2d/0x90
[ 0.000000] PGD 0
[ 0.000000] Oops: 0000 [#1] PREEMPT SMP
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.3.0-rc6+ #4
[ 0.000000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.7.5-20140531_083030-gandalf 04/01/2014
[ 0.000000] task: ffffffff819f7500 ti: ffffffff819e8000 task.ti:
ffffffff819e8000
[ 0.000000] RIP: 0010:[<ffffffff8100d19d>] [<ffffffff8100d19d>]
native_sched_clock+0x2d/0x90
[ 0.000000] RSP: 0000:ffffffff819ebee0 EFLAGS: 00010046
[ 0.000000] RAX: 0000000129f79c5a RBX: ffff88007b7d5c00 RCX: 0000000000000000
[ 0.000000] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff819f76e0
[ 0.000000] RBP: ffffffff819ebee0 R08: 0000000000000001 R09: 0000000000000000
[ 0.000000] R10: 0000000000000001 R11: ffffffff819f7500 R12: 0000000000000000
[ 0.000000] R13: 0000000000000000 R14: ffffffff819f7b30 R15: ffffffff819f7500
[ 0.000000] FS: 0000000000000000(0000) GS:ffff88007b600000(0000)
knlGS:0000000000000000
[ 0.000000] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 0.000000] CR2: 0000000000000000 CR3: 00000000019f2000 CR4: 00000000000406b0
[ 0.000000] Stack:
[ 0.000000] ffffffff819ebf28 ffffffff8108622f 0000000000000000
0000000000000086
[ 0.000000] ffffffff819f7500 0000000000000008 0000000000000008
00000000001d5c00
[ 0.000000] ffffffff0000ffff ffffffff819ebf58 ffffffff81cace4f
ffffffffffffffff
[ 0.000000] Call Trace:
[ 0.000000] [<ffffffff8108622f>] init_idle+0x13f/0x2d0
[ 0.000000] [<ffffffff81cace4f>] sched_init+0x304/0x345
[ 0.000000] [<ffffffff81c97d6d>] start_kernel+0x25e/0x417
[ 0.000000] [<ffffffff81c972fe>] x86_64_start_reservations+0x2a/0x2c
[ 0.000000] [<ffffffff81c97468>] x86_64_start_kernel+0x168/0x176
[ 0.000000] Code: 89 e5 48 83 e4 f0 0f 31 48 c1 e2 20 48 09 d0 65 ff 05 88
dd ff 7e 65 48 8b 35 e0 5b 1c 7f 65 48 8b 15 e0 5b 1c 7f 48 39 d6 75 2c <8b> 16
8b 4e 04 48 f7 e2 48 0f ad d0 48 d3 ea f6 c1 40 48 0f 45
[ 0.000000] RIP [<ffffffff8100d19d>] native_sched_clock+0x2d/0x90
[ 0.000000] RSP <ffffffff819ebee0>
[ 0.000000] CR2: 0000000000000000
[ 0.000000] ---[ end trace aff58b1304cfecf1 ]---
[ 0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
[ 0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle
task!
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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