From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D8CBC43331 for ; Thu, 2 Apr 2020 19:06:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 11E1D20719 for ; Thu, 2 Apr 2020 19:06:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388788AbgDBTGx (ORCPT ); Thu, 2 Apr 2020 15:06:53 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:38864 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732598AbgDBTGw (ORCPT ); Thu, 2 Apr 2020 15:06:52 -0400 Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jK5AO-0001Yn-7q; Thu, 02 Apr 2020 21:06:16 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 2444D100D52; Thu, 2 Apr 2020 21:06:15 +0200 (CEST) From: Thomas Gleixner To: Sean Christopherson Cc: x86@kernel.org, "Kenneth R . Crudup" , Paolo Bonzini , Fenghua Yu , Xiaoyao Li , Nadav Amit , Thomas Hellstrom , Tony Luck , Peter Zijlstra , Jessica Yu , Steven Rostedt , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] x86/split_lock: Refactor and export handle_user_split_lock() for KVM In-Reply-To: <20200402171946.GH13879@linux.intel.com> References: <20200402124205.334622628@linutronix.de> <20200402155554.27705-1-sean.j.christopherson@intel.com> <20200402155554.27705-3-sean.j.christopherson@intel.com> <87v9mhn7nf.fsf@nanos.tec.linutronix.de> <20200402171946.GH13879@linux.intel.com> Date: Thu, 02 Apr 2020 21:06:15 +0200 Message-ID: <87mu7tn1w8.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sean Christopherson writes: > On Thu, Apr 02, 2020 at 07:01:56PM +0200, Thomas Gleixner wrote: >> > static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {} >> > static inline void switch_to_sld(unsigned long tifn) {} >> > -static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code) >> > +static inline bool handle_user_split_lock(unsigned long ip) >> >> This is necessary because VMX can be compiled without CPU_SUP_INTEL? > > Ya, it came about when cleaning up the IA32_FEATURE_CONTROL MSR handling > to consolidate duplicate code. > > config KVM_INTEL > tristate "KVM for Intel (and compatible) processors support" > depends on KVM && IA32_FEAT_CTL > > config IA32_FEAT_CTL > def_bool y > depends on CPU_SUP_INTEL || CPU_SUP_CENTAUR || CPU_SUP_ZHAOXIN Ah, indeed. So something like the below would make sense. Hmm? Of course that can be mangled into Xiaoyao's patches, I'm not worried about my patch count :) Aside of that I really wish Intel HW folks had indicated the source of the #AC via the error code. It can only be 0 or 1 for the regular #AC so there would have been 31 bits to chose from. Thanks, tglx 8<---------------- --- a/arch/x86/include/asm/cpu.h +++ b/arch/x86/include/asm/cpu.h @@ -43,14 +43,14 @@ unsigned int x86_stepping(unsigned int s #ifdef CONFIG_CPU_SUP_INTEL extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c); extern void switch_to_sld(unsigned long tifn); -extern bool handle_user_split_lock(struct pt_regs *regs, long error_code); +extern int handle_ac_split_lock(unsigned long ip); extern void split_lock_validate_module_text(struct module *me, void *text, void *text_end); #else static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {} static inline void switch_to_sld(unsigned long tifn) {} -static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code) +static int handle_ac_split_lock(unsigned long ip) { - return false; + return -ENOSYS; } static inline void split_lock_validate_module_text(struct module *me, void *text, void *text_end) {} #endif --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -1102,13 +1102,20 @@ static void split_lock_init(void) split_lock_verify_msr(sld_state != sld_off); } -bool handle_user_split_lock(struct pt_regs *regs, long error_code) +int handle_ac_split_lock(unsigned long ip) { - if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal) - return false; + switch (sld_state) { + case sld_warn: + break; + case sld_off: + pr_warn_once("#AC: Spurious trap at address: 0x%lx\n", ip); + return -ENOSYS; + case sld_fatal: + return -EFAULT; + } pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n", - current->comm, current->pid, regs->ip); + current->comm, current->pid, ip); /* * Disable the split lock detection for this task so it can make @@ -1117,8 +1124,9 @@ bool handle_user_split_lock(struct pt_re */ sld_update_msr(false); set_tsk_thread_flag(current, TIF_SLD); - return true; + return 0; } +EXPORT_SYMBOL_GPL(handle_ac_split_lock); /* * This function is called only when switching between tasks with --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -304,7 +304,7 @@ dotraplinkage void do_alignment_check(st local_irq_enable(); - if (handle_user_split_lock(regs, error_code)) + if (!(regs->flags & X86_EFLAGS_AC) && !handle_ac_split_lock(regs->ip)) return; do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs, --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -65,6 +65,7 @@ MODULE_AUTHOR("Qumranet"); MODULE_LICENSE("GPL"); +MODULE_INFO(sld_safe, "Y"); #ifdef MODULE static const struct x86_cpu_id vmx_cpu_id[] = { @@ -4623,6 +4624,22 @@ static int handle_machine_check(struct k return 1; } +static bool guest_handles_ac(struct kvm_vcpu *vcpu) +{ + /* + * If guest has alignment checking enabled in CR0 and activated in + * eflags, then the #AC originated from CPL3 and the guest is able + * to handle it. It does not matter whether this is a regular or + * a split lock operation induced #AC. + */ + if (vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) && + kvm_get_rflags(vcpu) & X86_EFLAGS_AC) + return true; + + /* Add guest SLD handling checks here once it's supported */ + return false; +} + static int handle_exception_nmi(struct kvm_vcpu *vcpu) { struct vcpu_vmx *vmx = to_vmx(vcpu); @@ -4630,6 +4647,7 @@ static int handle_exception_nmi(struct k u32 intr_info, ex_no, error_code; unsigned long cr2, rip, dr6; u32 vect_info; + int err; vect_info = vmx->idt_vectoring_info; intr_info = vmx->exit_intr_info; @@ -4688,9 +4706,6 @@ static int handle_exception_nmi(struct k return handle_rmode_exception(vcpu, ex_no, error_code); switch (ex_no) { - case AC_VECTOR: - kvm_queue_exception_e(vcpu, AC_VECTOR, error_code); - return 1; case DB_VECTOR: dr6 = vmcs_readl(EXIT_QUALIFICATION); if (!(vcpu->guest_debug & @@ -4719,6 +4734,29 @@ static int handle_exception_nmi(struct k kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip; kvm_run->debug.arch.exception = ex_no; break; + case AC_VECTOR: + if (guest_handles_ac(vcpu)) { + kvm_queue_exception_e(vcpu, AC_VECTOR, error_code); + return 1; + } + /* + * Handle #AC caused by split lock detection. If the host + * mode is sld_warn, then it warns, marks current with + * TIF_SLD and disables split lock detection. So the guest + * can just continue. + * + * If the host mode is fatal, the handling code warned. Let + * qemu kill itself. + * + * If the host mode is off, then this #AC is bonkers and + * something is badly wrong. Let it fail as well. + */ + err = handle_ac_split_lock(kvm_rip_read(vcpu)); + if (!err) + return 1; + /* Propagate the error type to user space */ + error_code = err == -EFAULT ? 0x100 : 0x200; + fallthrough; default: kvm_run->exit_reason = KVM_EXIT_EXCEPTION; kvm_run->ex.exception = ex_no;