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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/entry/vdso/vclock_gettime.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/entry/vdso/vclock_gettime.c')
| -rw-r--r-- | arch/x86/entry/vdso/vclock_gettime.c | 15 |
1 files changed, 0 insertions, 15 deletions
diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c index 03c3eb77bfce..2f02d23a05ef 100644 --- a/arch/x86/entry/vdso/vclock_gettime.c +++ b/arch/x86/entry/vdso/vclock_gettime.c @@ -13,7 +13,6 @@ #include <uapi/linux/time.h> #include <asm/vgtod.h> -#include <asm/hpet.h> #include <asm/vvar.h> #include <asm/unistd.h> #include <asm/msr.h> @@ -28,16 +27,6 @@ extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts); extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz); extern time_t __vdso_time(time_t *t); -#ifdef CONFIG_HPET_TIMER -extern u8 hpet_page - __attribute__((visibility("hidden"))); - -static notrace cycle_t vread_hpet(void) -{ - return *(const volatile u32 *)(&hpet_page + HPET_COUNTER); -} -#endif - #ifdef CONFIG_PARAVIRT_CLOCK extern u8 pvclock_page __attribute__((visibility("hidden"))); @@ -195,10 +184,6 @@ notrace static inline u64 vgetsns(int *mode) if (gtod->vclock_mode == VCLOCK_TSC) cycles = vread_tsc(); -#ifdef CONFIG_HPET_TIMER - else if (gtod->vclock_mode == VCLOCK_HPET) - cycles = vread_hpet(); -#endif #ifdef CONFIG_PARAVIRT_CLOCK else if (gtod->vclock_mode == VCLOCK_PVCLOCK) cycles = vread_pvclock(mode); |