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([172.25.112.68]) by orsmga006.jf.intel.com with ESMTP; 11 Jan 2023 23:44:23 -0800 From: Xin Li 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, jgross@suse.com Subject: [PATCH v6 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index() Date: Wed, 11 Jan 2023 23:20:32 -0800 Message-Id: <20230112072032.35626-6-xin3.li@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230112072032.35626-1-xin3.li@intel.com> References: <20230112072032.35626-1-xin3.li@intel.com> MIME-Version: 1.0 X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1754802233385622679?= X-GMAIL-MSGID: =?utf-8?q?1754802233385622679?= From: "H. Peter Anvin (Intel)" 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) Signed-off-by: Xin Li --- Changes since v5: * Remove reviewers' SOBs (Borislav Petkov). Changes since v4: * Clear the LKGS feature from Xen PV guests (Juergen Gross). 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 replaced 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 + arch/x86/xen/enlighten_pv.c | 1 + 3 files changed, 31 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 9cfca3d7d0e2..b7ac85a1e5df 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1960,6 +1960,7 @@ void __init identify_boot_cpu(void) setup_cr_pinning(); tsx_init(); + lkgs_init(); } void identify_secondary_cpu(struct cpuinfo_x86 *c) diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c index 5b1379662877..ce2f19ee4bfc 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -276,6 +276,7 @@ static void __init xen_init_capabilities(void) setup_clear_cpu_cap(X86_FEATURE_ACC); setup_clear_cpu_cap(X86_FEATURE_X2APIC); setup_clear_cpu_cap(X86_FEATURE_SME); + setup_clear_cpu_cap(X86_FEATURE_LKGS); /* * Xen PV would need some work to support PCID: CR3 handling as well