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From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Lutomirski <luto@kernel.org>,
	"H . Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <ak@linux.intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Markus T Metzger <markus.t.metzger@intel.com>,
	Ravi Shankar <ravi.v.shankar@intel.com>,
	"Chang S . Bae" <chang.seok.bae@intel.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: [v3 07/12] x86/fsgsbase/64: Introduce the new FIND_PERCPU_BASE macro
Date: Tue, 23 Oct 2018 11:42:29 -0700	[thread overview]
Message-ID: <20181023184234.14025-8-chang.seok.bae@intel.com> (raw)
In-Reply-To: <20181023184234.14025-1-chang.seok.bae@intel.com>

GSBASE is used to find per-CPU data in the kernel. But when it 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.

Also, add the GAS-compatible RDPID macro.

The new macro will be used on a following patch.

Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/fsgsbase.h | 52 +++++++++++++++++++++++++++++++++
 arch/x86/include/asm/inst.h     | 15 ++++++++++
 2 files changed, 67 insertions(+)

diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h
index e500d771155f..0c2d7d8a8c01 100644
--- a/arch/x86/include/asm/fsgsbase.h
+++ b/arch/x86/include/asm/fsgsbase.h
@@ -111,6 +111,58 @@ extern void x86_gsbase_write_cpu_inactive(unsigned long gsbase);
 	MODRM 0xd0 wrgsbase_opd 1
 .endm
 
+#if CONFIG_SMP
+
+/*
+ * 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 FIND_PERCPU_BASE_RDPID reg:req
+	/*
+	 * The CPU/node NR is initialized earlier, directly in cpu_init().
+	 * The CPU NR is extracted from it.
+	 */
+	RDPID	\reg
+	andq	$VDSO_CPUNODE_MASK, \reg
+
+	/*
+	 * The kernel GSBASE value is found from the __per_cpu_offset table
+	 * with the CPU NR.
+	 */
+	movq	__per_cpu_offset(, \reg, 8), \reg
+.endm
+
+/*
+ * Same as above FIND_PERCPU_BASERDPID, except that CPU/node NR is loaded
+ * from the limit (size) field of a special segment descriptor entry in
+ * GDT.
+ */
+.macro FIND_PERCPU_BASE_SEG_LIMIT reg:req
+	/* Read CPU NR */
+	movq	$__CPUNODE_SEG, \reg
+	lsl	\reg, \reg
+	andq	$VDSO_CPUNODE_MASK, \reg
+
+	movq	__per_cpu_offset(, \reg, 8), \reg
+.endm
+
+.macro FIND_PERCPU_BASE reg:req
+	ALTERNATIVE \
+		"FIND_PERCPU_BASE_SEG_LIMIT \reg", \
+		"FIND_PERCPU_BASE_RDPID \reg", \
+		X86_FEATURE_RDPID
+.endm
+
+#else
+
+.macro FIND_PERCPU_BASE reg:req
+	/* Tracking the base offset value */
+	movq	pcpu_unit_offsets(%rip), \reg
+.endm
+
+#endif /* CONFIG_SMP */
+
 #endif /* CONFIG_X86_64 */
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/asm/inst.h b/arch/x86/include/asm/inst.h
index f5a796da07f8..d063841a17e3 100644
--- a/arch/x86/include/asm/inst.h
+++ b/arch/x86/include/asm/inst.h
@@ -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
-- 
2.19.1


  parent reply	other threads:[~2018-10-23 18:44 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-23 18:42 [v3 00/12] x86: Enable FSGSBASE instructions Chang S. Bae
2018-10-23 18:42 ` [v3 01/12] taint: Introduce a new taint flag (insecure) Chang S. Bae
2018-10-24 18:50   ` Andy Lutomirski
2018-10-23 18:42 ` [v3 02/12] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2018-10-24 18:51   ` Andy Lutomirski
2018-10-23 18:42 ` [v3 03/12] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions Chang S. Bae
2018-10-24 18:53   ` Andy Lutomirski
2018-10-24 19:21     ` Andi Kleen
2018-10-25 23:14       ` Andy Lutomirski
2018-10-25 23:31         ` Linus Torvalds
2018-10-26  0:09           ` Andy Lutomirski
2018-10-23 18:42 ` [v3 04/12] x86/fsgsbase/64: Enable FSGSBASE instructions in the helper functions Chang S. Bae
2018-10-24 19:16   ` Andy Lutomirski
2018-10-24 19:41     ` [Xen-devel] " Andrew Cooper
2018-10-25  6:09       ` Juergen Gross
2018-10-25 23:08         ` Andrew Cooper
2018-10-25 23:11           ` Andy Lutomirski
2018-10-25 23:14             ` Andrew Cooper
2018-10-25  7:32     ` Bae, Chang Seok
2018-10-25 23:00       ` Andy Lutomirski
2018-10-25 23:03         ` Bae, Chang Seok
2018-10-25 23:16     ` Andy Lutomirski
2018-10-23 18:42 ` [v3 05/12] x86/fsgsbase/64: Preserve FS/GS state in __switch_to() if FSGSBASE is on Chang S. Bae
2018-10-24 19:21   ` Andy Lutomirski
2018-10-24 19:36     ` Bae, Chang Seok
2018-10-23 18:42 ` [v3 06/12] x86/fsgsbase/64: When copying a thread, use the FSGSBASE instructions if available Chang S. Bae
2018-10-23 18:42 ` Chang S. Bae [this message]
2018-10-26  0:25   ` [v3 07/12] x86/fsgsbase/64: Introduce the new FIND_PERCPU_BASE macro Andy Lutomirski
2018-10-26  0:59     ` Nadav Amit
2018-10-23 18:42 ` [v3 08/12] x86/fsgsbase/64: Use the per-CPU base as GSBASE at the paranoid_entry Chang S. Bae
2018-10-23 18:42 ` [v3 09/12] selftests/x86/fsgsbase: Test WRGSBASE Chang S. Bae
2018-10-23 18:42 ` [v3 10/12] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2018-10-23 18:42 ` [v3 11/12] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2018-10-23 18:42 ` [v3 12/12] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae

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