[PATCH 3/6] x86: Add support for the clwb instruction

Ross Zwisler
2014-11-11T18:44:02Z

Add support for the new clwb instruction. This instruction was
announced in the document "Intel Architecture Instruction Set Extensions
Programming Reference" with reference number 319433-022.

https://software.intel.com/sites/default/files/managed/0d/53/319433-022.pdf

Here are some things of note:

- As with the clflushopt patches before this, I'm assuming that the addressing
mode generated by the original clflush instruction will match the new
clflush instruction with the 0x66 prefix for clflushopt, and for the
xsaveopt instruction with the 0x66 prefix for clwb. For all the test cases
that I've come up with and for the new clwb code generated by this patch
series, this has proven to be true on my test machine.

- According to the SDM, xsaveopt has a form where it has a REX.W prefix. I
believe that this prefix will not be generated by gcc in x86_64 kernel code.
Based on this, I don't believe I need to account for this extra prefix when
dealing with the assembly language created for clwb. Please correct me if
I'm wrong.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: H Peter Anvin <h.peter.anvin@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Cc: x86@kernel.org
---
arch/x86/include/asm/cpufeature.h | 1 +
arch/x86/include/asm/special_insns.h | 10 ++++++++++
2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index b3e6b89..fbbed34 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -227,6 +227,7 @@
#define X86_FEATURE_SMAP ( 9*32+20) /* Supervisor Mode Access Prevention */
#define X86_FEATURE_PCOMMIT ( 9*32+22) /* PCOMMIT instruction */
#define X86_FEATURE_CLFLUSHOPT ( 9*32+23) /* CLFLUSHOPT instruction */
+#define X86_FEATURE_CLWB ( 9*32+24) /* CLWB instruction */
#define X86_FEATURE_AVX512PF ( 9*32+26) /* AVX-512 Prefetch */
#define X86_FEATURE_AVX512ER ( 9*32+27) /* AVX-512 Exponential and Reciprocal */
#define X86_FEATURE_AVX512CD ( 9*32+28) /* AVX-512 Conflict Detection */
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 1709a2e..a328460 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -199,6 +199,16 @@ static inline void clflushopt(volatile void *__p)
"+m" (*(volatile char __force *)__p));
}

+static inline void clwb(volatile void *__p)
+{
+ alternative_io_2(".byte " __stringify(NOP_DS_PREFIX) "; clflush %P0",
+ ".byte 0x66; clflush %P0",
+ X86_FEATURE_CLFLUSHOPT,
+ ".byte 0x66; xsaveopt %P0",
+ X86_FEATURE_CLWB,
+ "+m" (*(volatile char __force *)__p));
+}
+
static inline void pcommit(void)
{
alternative(ASM_NOP4, ".byte 0x66, 0x0f, 0xae, 0xf8",
--
1.9.3