From: Alexandre Chartre <alexandre.chartre@oracle.com>
To: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Joel Fernandes <joel@joelfernandes.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Juergen Gross <jgross@suse.com>, Brian Gerst <brgerst@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Will Deacon <will@kernel.org>
Subject: Re: [patch V4 part 1 13/36] x86/kvm: Restrict ASYNC_PF to user space
Date: Wed, 6 May 2020 17:29:20 +0200 [thread overview]
Message-ID: <f52c0df3-943b-ef1a-092b-fa9621454d46@oracle.com> (raw)
In-Reply-To: <20200505134059.369802541@linutronix.de>
On 5/5/20 3:16 PM, Thomas Gleixner wrote:
> The async page fault injection into kernel space creates more problems than
> it solves. The host has absolutely no knowledge about the state of the
> guest if the fault happens in CPL0. The only restriction for the host is
> interrupt disabled state. If interrupts are enabled in the guest then the
> exception can hit arbitrary code. The HALT based wait in non-preemotible
> code is a hacky replacement for a proper hypercall.
>
> For the ongoing work to restrict instrumentation and make the RCU idle
> interaction well defined the required extra work for supporting async
> pagefault in CPL0 is just not justified and creates complexity for a
> dubious benefit.
>
> The CPL3 injection is well defined and does not cause any issues as it is
> more or less the same as a regular page fault from CPL3.
>
> Suggested-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/kernel/kvm.c | 100 +++-----------------------------------------------
> 1 file changed, 7 insertions(+), 93 deletions(-)
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
alex.
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -75,7 +75,6 @@ struct kvm_task_sleep_node {
> struct swait_queue_head wq;
> u32 token;
> int cpu;
> - bool use_halt;
> };
>
> static struct kvm_task_sleep_head {
> @@ -98,8 +97,7 @@ static struct kvm_task_sleep_node *_find
> return NULL;
> }
>
> -static bool kvm_async_pf_queue_task(u32 token, bool use_halt,
> - struct kvm_task_sleep_node *n)
> +static bool kvm_async_pf_queue_task(u32 token, struct kvm_task_sleep_node *n)
> {
> u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
> struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
> @@ -117,7 +115,6 @@ static bool kvm_async_pf_queue_task(u32
>
> n->token = token;
> n->cpu = smp_processor_id();
> - n->use_halt = use_halt;
> init_swait_queue_head(&n->wq);
> hlist_add_head(&n->link, &b->list);
> raw_spin_unlock(&b->lock);
> @@ -138,7 +135,7 @@ void kvm_async_pf_task_wait_schedule(u32
>
> lockdep_assert_irqs_disabled();
>
> - if (!kvm_async_pf_queue_task(token, false, &n))
> + if (!kvm_async_pf_queue_task(token, &n))
> return;
>
> for (;;) {
> @@ -154,91 +151,10 @@ void kvm_async_pf_task_wait_schedule(u32
> }
> EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait_schedule);
>
> -/*
> - * Invoked from the async page fault handler.
> - */
> -static void kvm_async_pf_task_wait_halt(u32 token)
> -{
> - struct kvm_task_sleep_node n;
> -
> - if (!kvm_async_pf_queue_task(token, true, &n))
> - return;
> -
> - for (;;) {
> - if (hlist_unhashed(&n.link))
> - break;
> - /*
> - * No point in doing anything about RCU here. Any RCU read
> - * side critical section or RCU watching section can be
> - * interrupted by VMEXITs and the host is free to keep the
> - * vCPU scheduled out as long as it sees fit. This is not
> - * any different just because of the halt induced voluntary
> - * VMEXIT.
> - *
> - * Also the async page fault could have interrupted any RCU
> - * watching context, so invoking rcu_irq_exit()/enter()
> - * around this is not gaining anything.
> - */
> - native_safe_halt();
> - local_irq_disable();
> - }
> -}
> -
> -/* Invoked from the async page fault handler */
> -static void kvm_async_pf_task_wait(u32 token, bool usermode)
> -{
> - bool can_schedule;
> -
> - /*
> - * No need to check whether interrupts were disabled because the
> - * host will (hopefully) only inject an async page fault into
> - * interrupt enabled regions.
> - *
> - * If CONFIG_PREEMPTION is enabled then check whether the code
> - * which triggered the page fault is preemptible. This covers user
> - * mode as well because preempt_count() is obviously 0 there.
> - *
> - * The check for rcu_preempt_depth() is also required because
> - * voluntary scheduling inside a rcu read locked section is not
> - * allowed.
> - *
> - * The idle task is already covered by this because idle always
> - * has a preempt count > 0.
> - *
> - * If CONFIG_PREEMPTION is disabled only allow scheduling when
> - * coming from user mode as there is no indication whether the
> - * context which triggered the page fault could schedule or not.
> - */
> - if (IS_ENABLED(CONFIG_PREEMPTION))
> - can_schedule = preempt_count() + rcu_preempt_depth() == 0;
> - else
> - can_schedule = usermode;
> -
> - /*
> - * If the kernel context is allowed to schedule then RCU is
> - * watching because no preemptible code in the kernel is inside RCU
> - * idle state. So it can be treated like user mode. User mode is
> - * safe because the #PF entry invoked enter_from_user_mode().
> - *
> - * For the non schedulable case invoke rcu_irq_enter() for
> - * now. This will be moved out to the pagefault entry code later
> - * and only invoked when really needed.
> - */
> - if (can_schedule) {
> - kvm_async_pf_task_wait_schedule(token);
> - } else {
> - rcu_irq_enter();
> - kvm_async_pf_task_wait_halt(token);
> - rcu_irq_exit();
> - }
> -}
> -
> static void apf_task_wake_one(struct kvm_task_sleep_node *n)
> {
> hlist_del_init(&n->link);
> - if (n->use_halt)
> - smp_send_reschedule(n->cpu);
> - else if (swq_has_sleeper(&n->wq))
> + if (swq_has_sleeper(&n->wq))
> swake_up_one(&n->wq);
> }
>
> @@ -337,8 +253,10 @@ bool __kvm_handle_async_pf(struct pt_reg
> panic("Host injected async #PF in interrupt disabled region\n");
>
> if (reason == KVM_PV_REASON_PAGE_NOT_PRESENT) {
> - /* page is swapped out by the host. */
> - kvm_async_pf_task_wait(token, user_mode(regs));
> + if (unlikely(!(user_mode(regs))))
> + panic("Host injected async #PF in kernel mode\n");
> + /* Page is swapped out by the host. */
> + kvm_async_pf_task_wait_schedule(token);
> } else {
> rcu_irq_enter();
> kvm_async_pf_task_wake(token);
> @@ -397,10 +315,6 @@ static void kvm_guest_cpu_init(void)
> 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;
> -#endif
> pa |= KVM_ASYNC_PF_ENABLED;
>
> if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF_VMEXIT))
>
next prev parent reply other threads:[~2020-05-06 15:33 UTC|newest]
Thread overview: 178+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 13:16 [patch V4 part 1 00/36] x86/entry: Entry/exception code rework, preparatory patches Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 01/36] rcu: Add comments marking transitions between RCU watching and not Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 02/36] x86/hw_breakpoint: Prevent data breakpoints on cpu_entry_area Thomas Gleixner
2020-05-06 8:14 ` Borislav Petkov
2020-05-06 12:11 ` Alexandre Chartre
2020-05-09 9:00 ` Lai Jiangshan
2020-05-09 9:23 ` Lai Jiangshan
2020-05-09 19:08 ` Andy Lutomirski
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Andy Lutomirski
2020-05-05 13:16 ` [patch V4 part 1 03/36] sched: Clean up scheduler_ipi() Thomas Gleixner
2020-05-06 8:32 ` Thomas Gleixner
2020-05-06 8:40 ` Borislav Petkov
2020-05-06 9:12 ` Thomas Gleixner
2020-05-06 10:02 ` Borislav Petkov
2020-05-06 12:37 ` Alexandre Chartre
2020-05-06 15:03 ` Thomas Gleixner
2020-05-06 15:33 ` Peter Zijlstra
2020-05-06 18:28 ` Paul E. McKenney
2020-05-06 18:37 ` Peter Zijlstra
2020-05-06 18:46 ` Paul E. McKenney
2020-05-12 15:13 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra (Intel)
2020-05-05 13:16 ` [patch V4 part 1 04/36] sched: Make scheduler_ipi inline Thomas Gleixner
2020-05-06 12:42 ` Alexandre Chartre
2020-05-12 15:13 ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 05/36] x86/entry: Flip _TIF_SIGPENDING and _TIF_NOTIFY_RESUME handling Thomas Gleixner
2020-05-06 11:53 ` Miroslav Benes
2020-05-06 12:06 ` Thomas Gleixner
2020-05-06 15:35 ` Peter Zijlstra
2020-05-06 13:06 ` Alexandre Chartre
2020-05-06 16:26 ` Borislav Petkov
2020-05-07 17:35 ` Andy Lutomirski
2020-05-13 20:56 ` Mathieu Desnoyers
2020-05-13 21:10 ` Steven Rostedt
2020-05-13 22:48 ` Mathieu Desnoyers
2020-05-14 0:12 ` Thomas Gleixner
2020-05-14 0:37 ` Steven Rostedt
2020-05-14 0:49 ` Thomas Gleixner
2020-05-14 1:22 ` Andy Lutomirski
2020-05-14 2:51 ` Mathieu Desnoyers
2020-05-14 9:19 ` Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 06/36] compiler: Simple READ/WRITE_ONCE() implementations Thomas Gleixner
2020-05-06 13:11 ` Alexandre Chartre
2020-05-06 13:33 ` Will Deacon
2020-05-06 15:36 ` Peter Zijlstra
2020-05-06 16:33 ` Borislav Petkov
2020-05-05 13:16 ` [patch V4 part 1 07/36] locking/atomics: Flip fallbacks and instrumentation Thomas Gleixner
2020-05-05 16:04 ` Mark Rutland
2020-05-07 23:41 ` Steven Rostedt
2020-05-08 8:40 ` Peter Zijlstra
2020-05-12 14:36 ` [tip: locking/kcsan] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 08/36] x86/doublefault: Remove memmove() call Thomas Gleixner
2020-05-06 13:47 ` Alexandre Chartre
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 09/36] x86/entry/64: Avoid pointless code when CONTEXT_TRACKING=n Thomas Gleixner
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 10/36] x86/entry: Remove the unused LOCKDEP_SYSEXIT cruft Thomas Gleixner
2020-05-06 13:52 ` Alexandre Chartre
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 11/36] x86/kvm: Handle async page faults directly through do_page_fault() Thomas Gleixner
2020-05-06 7:00 ` Paolo Bonzini
2020-05-06 14:05 ` Alexandre Chartre
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Andy Lutomirski
2020-05-05 13:16 ` [patch V4 part 1 12/36] x86/kvm: Sanitize kvm_async_pf_task_wait() Thomas Gleixner
2020-05-05 17:54 ` Paul E. McKenney
2020-05-05 21:50 ` Thomas Gleixner
2020-05-06 7:00 ` Paolo Bonzini
2020-05-06 12:53 ` Steven Rostedt
2020-05-06 15:13 ` Alexandre Chartre
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 13/36] x86/kvm: Restrict ASYNC_PF to user space Thomas Gleixner
2020-05-06 7:00 ` Paolo Bonzini
2020-05-06 15:29 ` Alexandre Chartre [this message]
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 14/36] x86/entry: Get rid of ist_begin/end_non_atomic() Thomas Gleixner
2020-05-06 15:34 ` Alexandre Chartre
2020-05-07 17:46 ` Andy Lutomirski
2020-05-13 22:57 ` Mathieu Desnoyers
2020-05-14 0:13 ` Steven Rostedt
2020-05-15 9:34 ` Thomas Gleixner
2020-05-15 13:11 ` Mathieu Desnoyers
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 15/36] kprobes: Lock kprobe_mutex while showing kprobe_blacklist Thomas Gleixner
2020-05-06 15:38 ` Alexandre Chartre
2020-05-12 15:18 ` [tip: core/kprobes] " tip-bot2 for Masami Hiramatsu
2020-05-05 13:16 ` [patch V4 part 1 16/36] kprobes: Support __kprobes blacklist in modules Thomas Gleixner
2020-05-06 15:47 ` Alexandre Chartre
2020-05-12 15:18 ` [tip: core/kprobes] " tip-bot2 for Masami Hiramatsu
2020-05-05 13:16 ` [patch V4 part 1 17/36] kprobes: Support NOKPROBE_SYMBOL() " Thomas Gleixner
2020-05-06 15:54 ` Alexandre Chartre
2020-05-12 15:18 ` [tip: core/kprobes] " tip-bot2 for Masami Hiramatsu
2020-05-05 13:16 ` [patch V4 part 1 18/36] samples/kprobes: Add __kprobes and NOKPROBE_SYMBOL() for handlers Thomas Gleixner
2020-05-06 15:57 ` Alexandre Chartre
2020-05-12 15:18 ` [tip: core/kprobes] " tip-bot2 for Masami Hiramatsu
2020-05-05 13:16 ` [patch V4 part 1 19/36] x86/entry: Exclude low level entry code from sanitizing Thomas Gleixner
2020-05-05 20:39 ` Brian Gerst
2020-05-06 15:42 ` Peter Zijlstra
2020-05-06 16:03 ` Alexandre Chartre
2020-05-13 22:58 ` Mathieu Desnoyers
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 20/36] vmlinux.lds.h: Create section for protection against instrumentation Thomas Gleixner
2020-05-06 16:08 ` Sean Christopherson
2020-05-06 16:28 ` Peter Zijlstra
2020-05-06 16:57 ` Thomas Gleixner
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 21/36] kprobes: Prevent probes in .noinstr.text section Thomas Gleixner
2020-05-08 6:30 ` Masami Hiramatsu
2020-05-19 19:52 ` [tip: core/kprobes] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 22/36] tracing: Provide lockdep less trace_hardirqs_on/off() variants Thomas Gleixner
2020-05-07 17:55 ` Andy Lutomirski
2020-05-07 18:52 ` Thomas Gleixner
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 23/36] bug: Annotate WARN/BUG/stackfail as noinstr safe Thomas Gleixner
2020-05-13 23:12 ` Mathieu Desnoyers
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-05 13:16 ` [patch V4 part 1 24/36] lockdep: Prepare for noinstr sections Thomas Gleixner
2020-05-08 0:23 ` Steven Rostedt
2020-05-08 8:44 ` Peter Zijlstra
2020-05-19 19:58 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 25/36] rcu/tree: Mark the idle relevant functions noinstr Thomas Gleixner
2020-05-05 18:07 ` Paul E. McKenney
2020-05-19 19:48 ` Joel Fernandes
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Thomas Gleixner
2020-09-28 22:22 ` Kim Phillips
2020-09-28 22:55 ` Paul E. McKenney
2020-09-29 7:25 ` Peter Zijlstra
2020-09-29 11:25 ` Peter Zijlstra
2020-09-29 14:34 ` Steven Rostedt
2020-09-29 14:52 ` Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 26/36] printk: Prepare for nested printk_nmi_enter() Thomas Gleixner
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Petr Mladek
2020-05-05 13:16 ` [patch V4 part 1 27/36] arm64: Prepare arch_nmi_enter() for recursion Thomas Gleixner
2020-05-13 23:28 ` Mathieu Desnoyers
2020-05-15 14:04 ` Frederic Weisbecker
2020-05-15 15:45 ` Will Deacon
2020-05-15 16:01 ` Mathieu Desnoyers
2020-05-15 21:29 ` Thomas Gleixner
2020-05-15 21:31 ` Frederic Weisbecker
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Frederic Weisbecker
2020-05-05 13:16 ` [patch V4 part 1 28/36] hardirq/nmi: Allow nested nmi_enter() Thomas Gleixner
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 29/36] x86/mce: Send #MC singal from task work Thomas Gleixner
2020-05-07 18:02 ` Andy Lutomirski
2020-05-08 8:48 ` Peter Zijlstra
2020-05-08 21:30 ` Andy Lutomirski
2020-05-14 14:16 ` Borislav Petkov
2020-05-13 23:42 ` Mathieu Desnoyers
2020-05-14 17:38 ` Thomas Gleixner
2020-05-14 17:42 ` Mathieu Desnoyers
2020-05-14 14:17 ` Borislav Petkov
2020-05-14 16:03 ` Mathieu Desnoyers
2020-05-14 16:19 ` Andy Lutomirski
2020-05-14 16:39 ` Borislav Petkov
2020-05-14 17:05 ` Mathieu Desnoyers
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 30/36] lockdep: Always inline lockdep_{off,on}() Thomas Gleixner
2020-05-13 23:46 ` Mathieu Desnoyers
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 31/36] printk: Disallow instrumenting print_nmi_enter() Thomas Gleixner
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 32/36] sh/ftrace: Move arch_ftrace_nmi_{enter,exit} into nmi exception Thomas Gleixner
2020-05-08 0:34 ` Steven Rostedt
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 33/36] x86,tracing: Robustify ftrace_nmi_enter() Thomas Gleixner
2020-05-08 6:19 ` Masami Hiramatsu
2020-05-05 13:16 ` [patch V4 part 1 34/36] sched,rcu,tracing: Avoid tracing before in_nmi() is correct Thomas Gleixner
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 35/36] x86: Replace ist_enter() with nmi_enter() Thomas Gleixner
2020-05-07 18:04 ` Andy Lutomirski
2020-05-07 18:17 ` Mathieu Desnoyers
2020-05-08 8:50 ` Peter Zijlstra
2020-05-08 17:12 ` Josh Poimboeuf
2020-05-14 0:12 ` Mathieu Desnoyers
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Peter Zijlstra
2020-05-05 13:16 ` [patch V4 part 1 36/36] rcu: Make RCU IRQ enter/exit functions rely on in_nmi() Thomas Gleixner
2020-05-05 18:13 ` Paul E. McKenney
2020-05-06 17:09 ` Alexandre Chartre
2020-05-19 19:52 ` [tip: core/rcu] " tip-bot2 for Paul E. McKenney
2020-05-07 18:05 ` [patch V4 part 1 00/36] x86/entry: Entry/exception code rework, preparatory patches Andy Lutomirski
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