Commit eaad9812 authored by Chang S. Bae's avatar Chang S. Bae Committed by Thomas Gleixner
Browse files

x86/entry/64: Introduce the FIND_PERCPU_BASE macro 



GSBASE is used to find per-CPU data in the kernel. But when GSBASE is
unknown, the per-CPU base can be found from the per_cpu_offset table with a
CPU NR.  The CPU NR is extracted from the limit field of the CPUNODE entry
in GDT, or by the RDPID instruction. This is a prerequisite for using
FSGSBASE in the low level entry code.

Also, add the GAS-compatible RDPID macro as binutils 2.23 do not support
it. Support is added in version 2.27.

[ tglx: Massaged changelog ]

Suggested-by: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1557309753-24073-12-git-send-email-chang.seok.bae@intel.com
Link: https://lkml.kernel.org/r/20200528201402.1708239-11-sashal@kernel.org
parent 96b23714

arch/x86/entry/calling.h

+34 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
#include <asm/percpu.h>

#include <asm/asm-offsets.h>

#include <asm/processor-flags.h>

#include <asm/inst.h>



/*
@@ -351,3 +352,36 @@ For 32-bit we have the following conventions - kernel is built with 
	call stackleak_erase

#endif

.endm



#ifdef CONFIG_SMP



/*

 * CPU/node NR is loaded from the limit (size) field of a special segment

 * descriptor entry in GDT.

 */

.macro LOAD_CPU_AND_NODE_SEG_LIMIT reg:req

	movq	$__CPUNODE_SEG, \reg

	lsl	\reg, \reg

.endm



/*

 * Fetch the per-CPU GSBASE value for this processor and put it in @reg.

 * We normally use %gs for accessing per-CPU data, but we are setting up

 * %gs here and obviously can not use %gs itself to access per-CPU data.

 */

.macro GET_PERCPU_BASE reg:req

	ALTERNATIVE \

		"LOAD_CPU_AND_NODE_SEG_LIMIT \reg", \

		"RDPID	\reg", \

		X86_FEATURE_RDPID

	andq	$VDSO_CPUNODE_MASK, \reg

	movq	__per_cpu_offset(, \reg, 8), \reg

.endm



#else



.macro GET_PERCPU_BASE reg:req

	movq	pcpu_unit_offsets(%rip), \reg

.endm



#endif /* CONFIG_SMP */

arch/x86/include/asm/inst.h

+15 −0
Original line number Diff line number Diff line
@@ -306,6 +306,21 @@ 
	.endif

	MODRM 0xc0 movq_r64_xmm_opd1 movq_r64_xmm_opd2

	.endm



.macro RDPID opd

	REG_TYPE rdpid_opd_type \opd

	.if rdpid_opd_type == REG_TYPE_R64

	R64_NUM rdpid_opd \opd

	.else

	R32_NUM rdpid_opd \opd

	.endif

	.byte 0xf3

	.if rdpid_opd > 7

	PFX_REX rdpid_opd 0

	.endif

	.byte 0x0f, 0xc7

	MODRM 0xc0 rdpid_opd 0x7

.endm

#endif



#endif

CRA Git | Maintained and supported by SUSTech CRA and CCSE