According to Intel RDTSC can be always synchronized with LFENCE
on all current CPUs. Implement the necessary CPUID bit for that.
It is unclear yet if that is true for all future CPUs too,
but if there's another way the kernel can be always updated.
Cc: asit.k.mallick@intel.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Changes to the last version:
- split implementation into two layers: ds/bts and ptrace
- renamed TIF's
- save/restore ds save area msr in __switch_to_xtra()
- make block-stepping only look at BTF bit
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Actually, on 386, cmpxchg and cmpxchg_local fall back on
cmpxchg_386_u8/16/32: it disables interruptions around non atomic
updates to mimic the cmpxchg behavior.
The comment:
/* Poor man's cmpxchg for 386. Unsuitable for SMP */
already present in cmpxchg_386_u32 tells much about how this cmpxchg
implementation should not be used in a SMP context. However, the cmpxchg_local
can perfectly use this fallback, since it only needs to be atomic wrt the local
cpu.
This patch adds a cmpxchg_486_u64 and uses it as a fallback for cmpxchg64
and cmpxchg64_local on 80386 and 80486.
Q:
but why is it called cmpxchg_486 when the other functions are called
A:
Because the standard cmpxchg is missing only on 386, but cmpxchg8b is
missing both on 386 and 486.
Citing Intel's Instruction set reference:
cmpxchg:
This instruction is not supported on Intel processors earlier than the
Intel486 processors.
cmpxchg8b:
This instruction encoding is not supported on Intel processors earlier
than the Pentium processors.
Q:
What's the reason to have cmpxchg64_local on 32 bit architectures?
Without that need all this would just be a few simple defines.
A:
cmpxchg64_local on 32 bits architectures takes unsigned long long
parameters, but cmpxchg_local only takes longs. Since we have cmpxchg8b
to execute a 8 byte cmpxchg atomically on pentium and +, it makes sense
to provide a flavor of cmpxchg and cmpxchg_local using this instruction.
Also, for 32 bits architectures lacking the 64 bits atomic cmpxchg, it
makes sense _not_ to define cmpxchg64 while cmpxchg could still be
available.
Moreover, the fallback for cmpxchg8b on i386 for 386 and 486 is a
However, cmpxchg64_local will be emulated by disabling interrupts on all
architectures where it is not supported atomically.
Therefore, we *could* turn cmpxchg64_local into a cmpxchg_local, but it
would make the 386/486 fallbacks ugly, make its design different from
cmpxchg/cmpxchg64 (which really depends on atomic operations and cannot
be emulated) and require the __cmpxchg_local to be expressed as a macro
rather than an inline function so the parameters would not be fixed to
unsigned long long in every case.
So I think cmpxchg64_local makes sense there, but I am open to
suggestions.
Q:
Are there any callers?
A:
I am actually using it in LTTng in my timestamping code. I use it to
work around CPUs with asynchronous TSCs. I need to update 64 bits
values atomically on this 32 bits architecture.
Changelog:
- Ran though checkpatch.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Fix following section mismatch warning:
WARNING: vmlinux.o(.text+0xc88c): Section mismatch: reference to .init.text:trap_init_f00f_bug (between 'init_intel' and 'cpuid4_cache_lookup')
init_intel are __cpuint where trap_init_f00f_bug is __init.
Fixed by declaring trap_init_f00f_bug __cpuinit.
Moved the defintion of trap_init_f00f_bug to the sole user in init.c
so the ugly prototype in intel.c could get killed.
Frank van Maarseveen <frankvm@frankvm.com> supplied the .config used
to reproduce the warning.
[ tglx: arch/x86 adaptation ]
Cc: Frank van Maarseveen <frankvm@frankvm.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Andi Kleen