Re: [PATCH v2] x86: Add kerneldoc for pcommit_sfence()

[Borislav Petkov]

On Tue, Apr 28, 2015 at 04:46:36PM -0600, Ross Zwisler wrote:
> Add kerneldoc comments for pcommit_sfence() describing the purpose of
> the pcommit instruction and demonstrating the usage of that instruction.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Cc: H Peter Anvin <h.peter.anvin@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> ---

Applied, thanks.

I added the "Example:" thing because apparently kernel-doc parses that,
see below.

Doing

$ scripts/kernel-doc -html arch/x86/include/asm/special_insns.h > /tmp/doc.html

and then looking at doc.html doesn't make me go all full of joy and clap my
hands but whatever, it is better than nothing.

---
From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Date: Tue, 28 Apr 2015 16:46:36 -0600
Subject: [PATCH] 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@xxxxxxxxxxxxxxx>
Cc: H Peter Anvin <h.peter.anvin@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1430261196-2401-1-git-send-email-ross.zwisler@xxxxxxxxxxxxxxx
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 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

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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