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x86/mm: Add kerneldoc comments for pcommit_sfence() 

Add kerneldoc comments for pcommit_sfence() describing the
purpose of the PCOMMIT instruction and demonstrating its usage
with an example.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H Peter Anvin <h.peter.anvin@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Link: http://lkml.kernel.org/r/1430261196-2401-1-git-send-email-ross.zwisler@linux.intel.com
Link: http://lkml.kernel.org/r/1431332153-18566-7-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ross Zwisler 2015-05-11 10:15:51 +02:00 committed by Ingo Molnar
parent 6c434d6176
commit ca7d9b795e
1 changed files with 38 additions and 0 deletions
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38
arch/x86/include/asm/special_insns.h
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@ -215,6 +215,44 @@ static inline void clwb(volatile void *__p)
: [pax] "a" (p));
}
/**
* pcommit_sfence() - persistent commit and fence
*
* The PCOMMIT instruction ensures that data that has been flushed from the
* processor's cache hierarchy with CLWB, CLFLUSHOPT or CLFLUSH is accepted to
* memory and is durable on the DIMM. The primary use case for this is
* persistent memory.
*
* This function shows how to properly use CLWB/CLFLUSHOPT/CLFLUSH and PCOMMIT
* with appropriate fencing.
*
* Example:
* void flush_and_commit_buffer(void *vaddr, unsigned int size)
* {
* unsigned long clflush_mask = boot_cpu_data.x86_clflush_size - 1;
* void *vend = vaddr + size;
* void *p;
*
* for (p = (void *)((unsigned long)vaddr & ~clflush_mask);
* p < vend; p += boot_cpu_data.x86_clflush_size)
* clwb(p);
*
* // SFENCE to order CLWB/CLFLUSHOPT/CLFLUSH cache flushes
* // MFENCE via mb() also works
* wmb();
*
* // PCOMMIT and the required SFENCE for ordering
* pcommit_sfence();
* }
*
* After this function completes the data pointed to by 'vaddr' has been
* accepted to memory and will be durable if the 'vaddr' points to persistent
* memory.
*
* PCOMMIT must always be ordered by an MFENCE or SFENCE, so to help simplify
* things we include both the PCOMMIT and the required SFENCE in the
* alternatives generated by pcommit_sfence().
*/
static inline void pcommit_sfence(void)
{
alternative(ASM_NOP7,