From: Xin Li <xin3.li@intel.com>
To: linux-kernel@vger.kernel.org, x86@kernel.org
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org,
brgerst@gmail.com, chang.seok.bae@intel.com
Subject: [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index()
Date: Wed, 19 Oct 2022 02:50:35 -0700 [thread overview]
Message-ID: <20221019095035.10823-6-xin3.li@intel.com> (raw)
In-Reply-To: <20221019095035.10823-1-xin3.li@intel.com>
From: "H. Peter Anvin (Intel)" <hpa@zytor.com>
The LKGS instruction atomically loads a segment descriptor into the
%gs descriptor registers, *except* that %gs.base is unchanged, and the
base is instead loaded into MSR_IA32_KERNEL_GS_BASE, which is exactly
what we want this function to do.
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
Changes since v3:
* We want less ASM not more, thus keep local_irq_save/restore() inside
native_load_gs_index() (Thomas Gleixner).
* For paravirt enabled kernels, initialize pv_ops.cpu.load_gs_index to
native_lkgs (Thomas Gleixner).
Changes since V2:
* Mark DI as input and output (+D) as in V1, since the exception handler
modifies it (Brian Gerst).
Changes since V1:
* Use EX_TYPE_ZERO_REG instead of fixup code in the obsolete .fixup code
section (Peter Zijlstra).
* Add a comment that states the LKGS_DI macro will be repalced with "lkgs %di"
once the binutils support the LKGS instruction (Peter Zijlstra).
---
arch/x86/include/asm/gsseg.h | 33 +++++++++++++++++++++++++++++----
arch/x86/kernel/cpu/common.c | 1 +
2 files changed, 30 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/gsseg.h b/arch/x86/include/asm/gsseg.h
index d15577c39e8d..ab6a595cea70 100644
--- a/arch/x86/include/asm/gsseg.h
+++ b/arch/x86/include/asm/gsseg.h
@@ -14,17 +14,42 @@
extern asmlinkage void asm_load_gs_index(u16 selector);
+/* Replace with "lkgs %di" once binutils support LKGS instruction */
+#define LKGS_DI _ASM_BYTES(0xf2,0x0f,0x00,0xf7)
+
+static inline void native_lkgs(unsigned int selector)
+{
+ u16 sel = selector;
+ asm_inline volatile("1: " LKGS_DI
+ _ASM_EXTABLE_TYPE_REG(1b, 1b, EX_TYPE_ZERO_REG, %k[sel])
+ : [sel] "+D" (sel));
+}
+
static inline void native_load_gs_index(unsigned int selector)
{
- unsigned long flags;
+ if (cpu_feature_enabled(X86_FEATURE_LKGS)) {
+ native_lkgs(selector);
+ } else {
+ unsigned long flags;
- local_irq_save(flags);
- asm_load_gs_index(selector);
- local_irq_restore(flags);
+ local_irq_save(flags);
+ asm_load_gs_index(selector);
+ local_irq_restore(flags);
+ }
}
#endif /* CONFIG_X86_64 */
+static inline void __init lkgs_init(void)
+{
+#ifdef CONFIG_PARAVIRT_XXL
+#ifdef CONFIG_X86_64
+ if (cpu_feature_enabled(X86_FEATURE_LKGS))
+ pv_ops.cpu.load_gs_index = native_lkgs;
+#endif
+#endif
+}
+
#ifndef CONFIG_PARAVIRT_XXL
static inline void load_gs_index(unsigned int selector)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3e508f239098..d6eb4f60b47d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1939,6 +1939,7 @@ void __init identify_boot_cpu(void)
setup_cr_pinning();
tsx_init();
+ lkgs_init();
}
void identify_secondary_cpu(struct cpuinfo_x86 *c)
--
2.34.1
next prev parent reply other threads:[~2022-10-19 12:02 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 9:50 [PATCH v4 0/5] Enable LKGS instruction Xin Li
2022-10-19 9:50 ` [PATCH v4 1/5] x86/cpufeature: add the cpu feature bit for LKGS Xin Li
2022-10-19 9:50 ` [PATCH v4 2/5] x86/opcode: add the LKGS instruction to x86-opcode-map Xin Li
2022-10-19 9:50 ` [PATCH v4 3/5] x86/gsseg: make asm_load_gs_index() take an u16 Xin Li
2022-10-19 9:50 ` [PATCH v4 4/5] x86/gsseg: move load_gs_index() to its own new header file Xin Li
2022-10-19 9:50 ` Xin Li [this message]
2022-10-19 12:16 ` [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index() Juergen Gross
2022-10-19 17:45 ` Li, Xin3
2022-10-19 18:01 ` H. Peter Anvin
2022-10-20 4:54 ` Juergen Gross
2022-10-20 6:05 ` Li, Xin3
2022-10-20 4:53 ` Juergen Gross
2022-10-20 5:58 ` Li, Xin3
2022-10-20 6:08 ` Juergen Gross
2022-10-20 6:24 ` Li, Xin3
2022-10-19 10:23 [PATCH v4 0/5] x86: Enable LKGS instruction Xin Li
2022-10-19 10:23 ` [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index() Xin Li
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