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 1/2] x86/cpu/AMD: Make LFENCE a serializing instruction
Date: Mon, 08 Jan 2018 16:09:21 -0600 [thread overview]
Message-ID: <20180108220921.12580.71694.stgit@tlendack-t1.amdoffice.net> (raw)
In-Reply-To: <20180108220912.12580.82330.stgit@tlendack-t1.amdoffice.net>
To aid in speculation control, make LFENCE a serializing instruction
since it has less overhead than MFENCE. This is done by setting bit 1
of MSR 0xc0011029 (DE_CFG). Some families that support LFENCE do not
have this MSR. For these families, the LFENCE instruction is already
serializing.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/include/asm/msr-index.h | 2 ++
arch/x86/kernel/cpu/amd.c | 10 ++++++++++
2 files changed, 12 insertions(+)
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index ab02261..1e7d710 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -352,6 +352,8 @@
#define FAM10H_MMIO_CONF_BASE_MASK 0xfffffffULL
#define FAM10H_MMIO_CONF_BASE_SHIFT 20
#define MSR_FAM10H_NODE_ID 0xc001100c
+#define MSR_F10H_DECFG 0xc0011029
+#define MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT 1
/* K8 MSRs */
#define MSR_K8_TOP_MEM1 0xc001001a
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index bcb75dc..5b438d8 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -829,6 +829,16 @@ static void init_amd(struct cpuinfo_x86 *c)
set_cpu_cap(c, X86_FEATURE_K8);
if (cpu_has(c, X86_FEATURE_XMM2)) {
+ /*
+ * A serializing LFENCE has less overhead than MFENCE, so
+ * use it for execution serialization. On families which
+ * don't have that MSR, LFENCE is already serializing.
+ * msr_set_bit() uses the safe accessors, too, even if the MSR
+ * is not present.
+ */
+ msr_set_bit(MSR_F10H_DECFG,
+ MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT);
+
/* MFENCE stops RDTSC speculation */
set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC);
}
next prev parent 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 [PATCH v2 0/2] x86/cpu/AMD: Make LFENCE a serializing instruction on AMD Tom Lendacky
2018-01-08 22:09 ` Tom Lendacky [this message]
2018-01-09 0:48 ` [tip:x86/pti] x86/cpu/AMD: Make LFENCE a serializing instruction 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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