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From: Borislav Petkov <>
To: "H. Peter Anvin" <>
Cc: Ross Zwisler <>,, Ingo Molnar <>,
	Thomas Gleixner <>
Subject: Re: [PATCH v2 0/2] add support for new persistent memory instructions
Date: Sat, 24 Jan 2015 12:14:30 +0100	[thread overview]
Message-ID: <20150124111430.GA10084@pd.tnic> (raw)
In-Reply-To: <>

On Fri, Jan 23, 2015 at 03:03:41PM -0800, H. Peter Anvin wrote:
> For the specific case of CLWB, we can use an "m" input rather than a
> "+m" output, simply because CLWB (or CLFLUSH* used as a standin for CLWB
> doesn't need to be ordered with respect to loads (whereas CLFLUSH* do).

Well, we could do something like:

        volatile struct { char x[64]; } *p = __p;

        if (static_cpu_has(X86_FEATURE_CLWB))
                asm volatile(".byte 0x66,0x0f,0xae,0x30" :: "m" (*p), "a" (p));
                asm volatile(ALTERNATIVE(
                        ".byte 0x3e; clflush (%[pax])",
                        ".byte 0x66; clflush (%[pax])", /* clflushopt (%%rax) */
                        : [p] "+m" (*p)
                        : [pax] "a" (p));

which would simplify the alternative macro too.

Generated asm looks ok to me (my objdump doesn't know CLWB yet :)):

0000000000000aa0 <myclflush>:
 aa0:   55                      push   %rbp
 aa1:   48 89 e5                mov    %rsp,%rbp
 aa4:   eb 0a                   jmp    ab0 <myclflush+0x10>
 aa6:   48 89 f8                mov    %rdi,%rax
 aa9:   66 0f ae 30             data16 xsaveopt (%rax)
 aad:   5d                      pop    %rbp
 aae:   c3                      retq
 aaf:   90                      nop
 ab0:   48 89 f8                mov    %rdi,%rax
 ab3:   3e 0f ae 38             clflush %ds:(%rax)
 ab7:   5d                      pop    %rbp
 ab8:   c3                      retq

> Should we use an SFENCE as a standin if pcommit is unavailable, in case
> we end up using CLFLUSHOPT?

Btw, is PCOMMIT a lightweight SFENCE for this persistent memory aspect
to make sure stuff has become persistent after executing it? But not all
stuff like SFENCE so SFENCE is the bigger hammer?


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

  reply	other threads:[~2015-01-24 11:14 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-23 20:40 Ross Zwisler
2015-01-23 20:40 ` [PATCH v2 1/2] x86: Add support for the pcommit instruction Ross Zwisler
2015-01-23 20:40 ` [PATCH v2 2/2] x86: Add support for the clwb instruction Ross Zwisler
2015-01-23 23:03 ` [PATCH v2 0/2] add support for new persistent memory instructions H. Peter Anvin
2015-01-24 11:14   ` Borislav Petkov [this message]
2015-01-26 19:59     ` Ross Zwisler
2015-01-26 21:34       ` Borislav Petkov
2015-01-26 21:50         ` Ross Zwisler
2015-01-26 22:39           ` Borislav Petkov
2015-01-26 23:14             ` Ross Zwisler
2015-01-26 19:51   ` Ross Zwisler
2015-01-26 20:05     ` H. Peter Anvin

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