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x86/entry/64: Introduce the FIND_PERCPU_BASE macro

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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: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Thomas 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
This commit is contained in:
Chang S. Bae 2020-05-28 16:13:56 -04:00 committed by Thomas Gleixner
parent 96b2371413
commit eaad981291
2 changed files with 49 additions and 0 deletions
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34
arch/x86/entry/calling.h
View File

@ -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 */

15
arch/x86/include/asm/inst.h
View File

@ -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