x86/cpu/AMD: Make LFENCE a serializing instruction

commit e4d0e84e490790798691aaa0f2e598637f1867ec upstream.

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Paul Turner <pjt@google.com>
Link: https://lkml.kernel.org/r/20180108220921.12580.71694.stgit@tlendack-t1.amdoffice.net
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 3d48aa4..98274c1 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -150,6 +150,8 @@
 #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 60d4c33..7e66b7d 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -641,6 +641,16 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
                set_cpu_cap(c, X86_FEATURE_K8);
 
        if (cpu_has_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);
        }