From: Borislav Petkov <bp@alien8.de>
To: Dave Jiang <dave.jiang@intel.com>
Cc: vkoul@kernel.org, tglx@linutronix.de, mingo@redhat.com,
dan.j.williams@intel.com, tony.luck@intel.com,
jing.lin@intel.com, ashok.raj@intel.com,
sanjay.k.kumar@intel.com, fenghua.yu@intel.com,
kevin.tian@intel.com, David.Laight@ACULAB.COM,
dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
Michael Matz <matz@suse.de>
Subject: Re: [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage
Date: Thu, 24 Sep 2020 15:07:46 +0200 [thread overview]
Message-ID: <20200924130746.GF5030@zn.tnic> (raw)
In-Reply-To: <160090264332.44288.7575027054245105525.stgit@djiang5-desk3.ch.intel.com>
On Wed, Sep 23, 2020 at 04:10:43PM -0700, Dave Jiang wrote:
> +/* The dst parameter must be 64-bytes aligned */
> +static inline void movdir64b(void *dst, const void *src)
> +{
> + /*
> + * Note that this isn't an "on-stack copy", just definition of "dst"
> + * as a pointer to 64-bytes of stuff that is going to be overwritten.
> + * In the MOVDIR64B case that may be needed as you can use the
> + * MOVDIR64B instruction to copy arbitrary memory around. This trick
> + * lets the compiler know how much gets clobbered.
> + */
> + volatile struct { char _[64]; } *__dst = dst;
> +
> + /* MOVDIR64B [rdx], rax */
> + asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
> + :
> + : "m" (*(struct { char _[64];} **)src), "a" (__dst)
> + : "memory");
> +}
Ok, Micha and I hashed it out on IRC, here's what you do. Please keep
the comments too because we will forget soon again.
static inline void movdir64b(void *__dst, const void *src)
{
struct { char _[64]; } *__src = src;
struct { char _[64]; } *__dst = dst;
/*
* MOVDIR64B %(rdx), rax.
*
* Both __src and __dst must be memory constraints in order to tell the
* compiler that no other memory accesses should be reordered around
* this one.
*
* Also, both must be supplied as lvalues because this tells
* the compiler what the object is (its size) the instruction accesses.
* I.e., not the pointers but what they point, thus the deref'ing '*'.
*/
asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
: "+m" (*__dst)
: "m" (*__src), "a" (__dst), "d" (__src));
}
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2020-09-24 13:07 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <160090233730.44288.4446779116422752486.stgit@djiang5-desk3.ch.intel.com>
2020-09-23 23:10 ` [PATCH v5 3/5] dmaengine: idxd: Add shared workqueue support Dave Jiang
2020-09-23 23:11 ` [PATCH v5 4/5] dmaengine: idxd: Clean up descriptors with fault error Dave Jiang
2020-09-23 23:11 ` [PATCH v5 5/5] dmaengine: idxd: Add ABI documentation for shared wq Dave Jiang
[not found] ` <160090264332.44288.7575027054245105525.stgit@djiang5-desk3.ch.intel.com>
2020-09-24 8:24 ` [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage David Laight
2020-09-24 10:15 ` Borislav Petkov
2020-09-24 10:42 ` David Laight
2020-09-24 11:02 ` Borislav Petkov
2020-09-24 11:25 ` David Laight
2020-09-24 14:07 ` Michael Matz
2020-09-24 13:07 ` Borislav Petkov [this message]
2020-09-24 13:27 ` David Laight
2020-09-24 15:07 ` Dave Jiang
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