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| author |   Andy Lutomirski <luto@kernel.org> | 2016-04-07 17:16:59 -0700 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2016-04-13 10:28:34 +0200 |
| commit | 1ed95e52d902035e39a715ff3a314a893a96e5b7 (patch) | |
| tree | 6e06e68794f1cd7db67e3fa1a568e15d92ce71ae /arch/x86/kernel/hpet.c | |
| parent | x86/entry/64: Make gs_change a local label (diff) | |
| download | linux-dev-1ed95e52d902035e39a715ff3a314a893a96e5b7.tar.xz linux-dev-1ed95e52d902035e39a715ff3a314a893a96e5b7.zip | |
x86/vdso: Remove direct HPET access through the vDSO
Allowing user code to map the HPET is problematic. HPET
implementations are notoriously buggy, and there are probably many
machines on which even MMIO reads from bogus HPET addresses are
problematic.
We have a report that the Dell Precision M2800 with:
ACPI: HPET 0x00000000C8FE6238 000038 (v01 DELL CBX3 01072009 AMI. 00000005)
is either so slow when accessing the HPET or actually hangs in some
regard, causing soft lockups to be reported if users do unexpected
things to the HPET.
The vclock HPET code has also always been a questionable speedup.
Accessing an HPET is exceedingly slow (on the order of several
microseconds), so the added overhead in requiring a syscall to read
the HPET is a small fraction of the total code of accessing it.
To avoid future problems, let's just delete the code entirely.
In the long run, this could actually be a speedup. Waiman Long as a
patch to optimize the case where multiple CPUs contend for the HPET,
but that won't help unless all the accesses are mediated by the
kernel.
Reported-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <Waiman.Long@hpe.com>
Cc: Waiman Long <waiman.long@hpe.com>
Link: http://lkml.kernel.org/r/d2f90bba98db9905041cff294646d290d378f67a.1460074438.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/hpet.c')
| -rw-r--r-- | arch/x86/kernel/hpet.c | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index a1f0e4a5c47e..7282c2e3858e 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -773,7 +773,6 @@ static struct clocksource clocksource_hpet = { .mask = HPET_MASK, .flags = CLOCK_SOURCE_IS_CONTINUOUS, .resume = hpet_resume_counter, - .archdata = { .vclock_mode = VCLOCK_HPET }, }; static int hpet_clocksource_register(void) |