From patchwork Sat Feb 29 17:50:33 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andy Lutomirski X-Patchwork-Id: 11413971 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 23B6F92A for ; Sat, 29 Feb 2020 17:50:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DFE3E24677 for ; Sat, 29 Feb 2020 17:50:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582998641; bh=b5d53c1LMiAPYIbaFIs3eRDSbWhifBbrJXJEQtRut0Q=; h=From:To:Cc:Subject:Date:List-ID:From; b=xrvl7QTeDVVzY3I26aRQKAaQ39pGYJZNgBQ0zm0SNB1YeQ0bR/GcMvN4Iq/l6PNwI MEFbDKGvQdsmQ3B0F9g6nudMHgqv/NqARVkX5l2grw0IakR2Q2yNDKu8ZZo6y5OThN dbhxp0WV86rq6AS1OAt40Ie1mDhtbpCRxs8v5oXo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727387AbgB2Ruf (ORCPT ); Sat, 29 Feb 2020 12:50:35 -0500 Received: from mail.kernel.org ([198.145.29.99]:51424 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727194AbgB2Ruf (ORCPT ); Sat, 29 Feb 2020 12:50:35 -0500 Received: from localhost (c-67-180-165-146.hsd1.ca.comcast.net [67.180.165.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4D55224677; Sat, 29 Feb 2020 17:50:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582998634; bh=b5d53c1LMiAPYIbaFIs3eRDSbWhifBbrJXJEQtRut0Q=; h=From:To:Cc:Subject:Date:From; b=PcBJaU+kuEs+f8TG7dYfEBfRgMrAaz3sMSzrTYduXH1PxkRSUCT3KjVDKFEIWCN65 6ynj91NLb6Ih1A6vuYp0boHx5h9nYw9EzUbbgYgkcnCBcVOIHEi4JvojMAIepLZQaG wEfV1uLeaBa4Mk9zmX56c43oKFC1jpVvkxSRUt9o= From: Andy Lutomirski To: LKML , x86@kernel.org, kvm list , Paolo Bonzini Cc: Andy Lutomirski Subject: [PATCH v2] x86/kvm: Handle async page faults directly through do_page_fault() Date: Sat, 29 Feb 2020 09:50:33 -0800 Message-Id: <53626d08de5df34eacce80cb74f19a06fdc690c6.1582998497.git.luto@kernel.org> X-Mailer: git-send-email 2.24.1 MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org KVM overloads #PF to indicate two types of not-actually-page-fault events. Right now, the KVM guest code intercepts them by modifying the IDT and hooking the #PF vector. This makes the already fragile fault code even harder to understand, and it also pollutes call traces with async_page_fault and do_async_page_fault for normal page faults. Clean it up by moving the logic into do_page_fault() using a static branch. This gets rid of the platform trap_init override mechanism completely. Signed-off-by: Andy Lutomirski --- Changes from v1: improve comments (Paolo, Andrew Cooper) arch/x86/entry/entry_64.S | 4 ---- arch/x86/include/asm/kvm_para.h | 17 +++++++++++++++- arch/x86/include/asm/x86_init.h | 2 -- arch/x86/kernel/kvm.c | 36 +++++++++++++++++++-------------- arch/x86/kernel/traps.c | 2 -- arch/x86/kernel/x86_init.c | 1 - arch/x86/mm/fault.c | 23 +++++++++++++++++++++ 7 files changed, 60 insertions(+), 25 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index f2bb91e87877..be1fc6f2fe85 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1202,10 +1202,6 @@ idtentry xendebug do_debug has_error_code=0 idtentry general_protection do_general_protection has_error_code=1 idtentry page_fault do_page_fault has_error_code=1 read_cr2=1 -#ifdef CONFIG_KVM_GUEST -idtentry async_page_fault do_async_page_fault has_error_code=1 read_cr2=1 -#endif - #ifdef CONFIG_X86_MCE idtentry machine_check do_mce has_error_code=0 paranoid=1 #endif diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h index 9b4df6eaa11a..4d72f5488584 100644 --- a/arch/x86/include/asm/kvm_para.h +++ b/arch/x86/include/asm/kvm_para.h @@ -92,7 +92,17 @@ void kvm_async_pf_task_wait(u32 token, int interrupt_kernel); void kvm_async_pf_task_wake(u32 token); u32 kvm_read_and_reset_pf_reason(void); extern void kvm_disable_steal_time(void); -void do_async_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address); +extern bool do_kvm_handle_async_pf(struct pt_regs *regs, unsigned long error_code, unsigned long address); + +DECLARE_STATIC_KEY_FALSE(kvm_async_pf_enabled); + +static inline bool kvm_handle_async_pf(struct pt_regs *regs, unsigned long error_code, unsigned long address) +{ + if (static_branch_unlikely(&kvm_async_pf_enabled)) + return do_kvm_handle_async_pf(regs, error_code, address); + else + return false; +} #ifdef CONFIG_PARAVIRT_SPINLOCKS void __init kvm_spinlock_init(void); @@ -130,6 +140,11 @@ static inline void kvm_disable_steal_time(void) { return; } + +static inline bool kvm_handle_async_pf(struct pt_regs *regs, unsigned long error_code, unsigned long address) +{ + return false; +} #endif #endif /* _ASM_X86_KVM_PARA_H */ diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h index 96d9cd208610..6807153c0410 100644 --- a/arch/x86/include/asm/x86_init.h +++ b/arch/x86/include/asm/x86_init.h @@ -50,14 +50,12 @@ struct x86_init_resources { * @pre_vector_init: init code to run before interrupt vectors * are set up. * @intr_init: interrupt init code - * @trap_init: platform specific trap setup * @intr_mode_select: interrupt delivery mode selection * @intr_mode_init: interrupt delivery mode setup */ struct x86_init_irqs { void (*pre_vector_init)(void); void (*intr_init)(void); - void (*trap_init)(void); void (*intr_mode_select)(void); void (*intr_mode_init)(void); }; diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index d817f255aed8..93ab0cbd304e 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -35,6 +35,8 @@ #include #include +DEFINE_STATIC_KEY_FALSE(kvm_async_pf_enabled); + static int kvmapf = 1; static int __init parse_no_kvmapf(char *arg) @@ -242,25 +244,29 @@ u32 kvm_read_and_reset_pf_reason(void) EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason); NOKPROBE_SYMBOL(kvm_read_and_reset_pf_reason); -dotraplinkage void -do_async_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address) +bool +do_kvm_handle_async_pf(struct pt_regs *regs, unsigned long error_code, unsigned long address) { + /* + * If we get a page fault right here, the pf_reason seems likely + * to be clobbered. Bummer. + */ + switch (kvm_read_and_reset_pf_reason()) { default: - do_page_fault(regs, error_code, address); - break; + return false; case KVM_PV_REASON_PAGE_NOT_PRESENT: /* page is swapped out by the host. */ kvm_async_pf_task_wait((u32)address, !user_mode(regs)); - break; + return true; case KVM_PV_REASON_PAGE_READY: rcu_irq_enter(); kvm_async_pf_task_wake((u32)address); rcu_irq_exit(); - break; + return true; } } -NOKPROBE_SYMBOL(do_async_page_fault); +NOKPROBE_SYMBOL(do_kvm_handle_async_pf); static void __init paravirt_ops_setup(void) { @@ -306,7 +312,11 @@ static notrace void kvm_guest_apic_eoi_write(u32 reg, u32 val) static void kvm_guest_cpu_init(void) { if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) { - u64 pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason)); + u64 pa; + + WARN_ON_ONCE(!static_branch_likely(&kvm_async_pf_enabled)); + + pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason)); #ifdef CONFIG_PREEMPTION pa |= KVM_ASYNC_PF_SEND_ALWAYS; @@ -570,11 +580,6 @@ static int kvm_cpu_down_prepare(unsigned int cpu) } #endif -static void __init kvm_apf_trap_init(void) -{ - update_intr_gate(X86_TRAP_PF, async_page_fault); -} - static DEFINE_PER_CPU(cpumask_var_t, __pv_tlb_mask); static void kvm_flush_tlb_others(const struct cpumask *cpumask, @@ -611,8 +616,6 @@ static void __init kvm_guest_init(void) register_reboot_notifier(&kvm_pv_reboot_nb); for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) raw_spin_lock_init(&async_pf_sleepers[i].lock); - if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF)) - x86_init.irqs.trap_init = kvm_apf_trap_init; if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { has_steal_clock = 1; @@ -652,6 +655,9 @@ static void __init kvm_guest_init(void) * overcommitted. */ hardlockup_detector_disable(); + + if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) + static_branch_enable(&kvm_async_pf_enabled); } static noinline uint32_t __kvm_cpuid_base(void) diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 6ef00eb6fbb9..bcb514c801f2 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -936,7 +936,5 @@ void __init trap_init(void) idt_setup_ist_traps(); - x86_init.irqs.trap_init(); - idt_setup_debugidt_traps(); } diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c index 85f1a90c55cd..123f1c1f1788 100644 --- a/arch/x86/kernel/x86_init.c +++ b/arch/x86/kernel/x86_init.c @@ -79,7 +79,6 @@ struct x86_init_ops x86_init __initdata = { .irqs = { .pre_vector_init = init_ISA_irqs, .intr_init = native_init_IRQ, - .trap_init = x86_init_noop, .intr_mode_select = apic_intr_mode_select, .intr_mode_init = apic_intr_mode_init }, diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index fa4ea09593ab..c2e4661c1f8b 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -30,6 +30,7 @@ #include /* store_idt(), ... */ #include /* exception stack */ #include /* VMALLOC_START, ... */ +#include /* kvm_handle_async_pf */ #define CREATE_TRACE_POINTS #include @@ -1505,6 +1506,28 @@ do_page_fault(struct pt_regs *regs, unsigned long hw_error_code, unsigned long address) { prefetchw(¤t->mm->mmap_sem); + /* + * KVM has two types of events that are not actual page faults but + * are, unfortunately, delivered using the #PF vector. These events + * are "you just accessed valid memory, but the host doesn't have it + * right now, so I'll put you to sleep if you continue" and "the + * memory you tried to access earlier is available now." + * + * We are relying on the interrupted context being sane (valid RSP, + * relevant locks not held, etc.), which is okay if the interrupted + * context is user mode or has IF=1. We are also relying on the KVM + * async pf type field and CR2 being read consistently instead of + * getting values from real and async page faults mixed up. + * + * There is at least one situation in which these events can be + * delivered regardless of EFLAGS.IF: writing to MSR_KVM_ASYNC_PF_EN + * can synchronously deliver wakeup events. + * + * Fingers crossed. + */ + if (kvm_handle_async_pf(regs, hw_error_code, address)) + return; + trace_page_fault_entries(regs, hw_error_code, address); if (unlikely(kmmio_fault(regs, address)))