From: Tom Lendacky <thomas.lendacky@amd.com>
To: x86@kernel.org, linux-kernel@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>,
Tim Chen <tim.c.chen@linux.intel.com>,
Greg Kroah-Hartman <gregkh@linux-foundation.org>,
David Woodhouse <dwmw@amazon.co.uk>, Paul Turner <pjt@google.com>
Subject: [PATCH v2 0/2] x86/cpu/AMD: Make LFENCE a serializing instruction on AMD
Date: Mon, 08 Jan 2018 16:09:12 -0600 [thread overview]
Message-ID: <20180108220912.12580.82330.stgit@tlendack-t1.amdoffice.net> (raw)
To aid in speculation control, the LFENCE instruction will be turned into
a serializing instruction. There is less performance impact using LFENCE
in this way compared to MFENCE.
With LFENCE now being a serializing instruction, it can be also used in
rdtsc_ordered() in preference to MFENCE_RDTSC. Since the kernel could
be running under a hypervisor that does not allow writing to that MSR,
it must be first verified that the write was successful before setting
the LFENCE_RDTSC feature.
The following patches are included in this series:
- Make LFENCE a serializing instruction on AMD
- Use LFENCE_RDTSC in preference to MFENCE_RDTSC on AMD
This patch series is based on tip:x86/pti.
---
Changes from v1:
- Add a check verifying the MSR was actually updated
- Remove the third patch that eliminates the MFENCE_RDTSC feature
(since the feature is still needed)
- Adding Dan Williams to the cc since this will impact nospec_barrier(),
which will require an alternative_2 to add an MFENCE instruction with
an MFENCE_RDTSC check
Tom Lendacky (2):
x86/cpu/AMD: Make LFENCE a serializing instruction
x86/cpu/AMD: Use LFENCE_RDTSC in preference to MFENCE_RDTSC
arch/x86/include/asm/msr-index.h | 3 +++
arch/x86/kernel/cpu/amd.c | 27 +++++++++++++++++++++++++--
2 files changed, 28 insertions(+), 2 deletions(-)
--
Tom Lendacky
next reply other threads:[~2018-01-08 22:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-08 22:09 Tom Lendacky [this message]
2018-01-08 22:09 ` [PATCH v2 1/2] x86/cpu/AMD: Make LFENCE a serializing instruction Tom Lendacky
2018-01-09 0:48 ` [tip:x86/pti] " tip-bot for Tom Lendacky
2018-01-08 22:09 ` [PATCH v2 2/2] x86/cpu/AMD: Use LFENCE_RDTSC in preference to MFENCE_RDTSC Tom Lendacky
2018-01-09 0:49 ` [tip:x86/pti] " tip-bot for Tom Lendacky
2018-01-08 22:34 ` [PATCH v2 0/2] x86/cpu/AMD: Make LFENCE a serializing instruction on AMD Dan Williams
2018-01-08 23:52 ` Borislav Petkov
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