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Subject[tip:x86/mm] x86/mm: Add kerneldoc comments for pcommit_sfence()
Commit-ID:  ca7d9b795e6bc78c80a1771ada867994fabcfc01
Gitweb: http://git.kernel.org/tip/ca7d9b795e6bc78c80a1771ada867994fabcfc01
Author: Ross Zwisler <ross.zwisler@linux.intel.com>
AuthorDate: Mon, 11 May 2015 10:15:51 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 11 May 2015 10:38:44 +0200

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>
---
arch/x86/include/asm/special_insns.h | 38 ++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)

diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index aeb4666e..2270e41 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -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,

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