[PATCH 2/5] x86/mm: Add kerneldoc comments for pcommit_sfence()

Borislav Petkov
2015-05-11T08:17:09Z

From: Ross Zwisler <ross.zwisler@linux.intel.com>

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>
Cc: H Peter Anvin <h.peter.anvin@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/1430261196-2401-1-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: Borislav Petkov <bp@suse.de>
---
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 aeb4666e0c0a..2270e41b32fd 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,
--
2.3.5