Re: [PATCH v7 08/12] Handle async PF in a guest.

[Jan Kiszka <jan.kiszka@siemens.com>]

Am 14.10.2010 11:22, Gleb Natapov wrote:
> When async PF capability is detected hook up special page fault handler
> that will handle async page fault events and bypass other page faults to
> regular page fault handler. Also add async PF handling to nested SVM
> emulation. Async PF always generates exit to L1 where vcpu thread will
> be scheduled out until page is available.
> 
> Acked-by: Rik van Riel <riel@redhat.com>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> ---
>  arch/x86/include/asm/kvm_para.h |   12 +++
>  arch/x86/include/asm/traps.h    |    1 +
>  arch/x86/kernel/entry_32.S      |   10 ++
>  arch/x86/kernel/entry_64.S      |    3 +
>  arch/x86/kernel/kvm.c           |  181 +++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/svm.c              |   45 ++++++++--
>  6 files changed, 243 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 2315398..fbfd367 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -65,6 +65,9 @@ struct kvm_mmu_op_release_pt {
>  	__u64 pt_phys;
>  };
>  
> +#define KVM_PV_REASON_PAGE_NOT_PRESENT 1
> +#define KVM_PV_REASON_PAGE_READY 2
> +
>  struct kvm_vcpu_pv_apf_data {
>  	__u32 reason;
>  	__u8 pad[60];
> @@ -171,8 +174,17 @@ static inline unsigned int kvm_arch_para_features(void)
>  
>  #ifdef CONFIG_KVM_GUEST
>  void __init kvm_guest_init(void);
> +void kvm_async_pf_task_wait(u32 token);
> +void kvm_async_pf_task_wake(u32 token);
> +u32 kvm_read_and_reset_pf_reason(void);
>  #else
>  #define kvm_guest_init() do { } while (0)
> +#define kvm_async_pf_task_wait(T) do {} while(0)
> +#define kvm_async_pf_task_wake(T) do {} while(0)
> +static u32 kvm_read_and_reset_pf_reason(void)
> +{
> +	return 0;
> +}
>  #endif
>  
>  #endif /* __KERNEL__ */
> diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
> index f66cda5..0310da6 100644
> --- a/arch/x86/include/asm/traps.h
> +++ b/arch/x86/include/asm/traps.h
> @@ -30,6 +30,7 @@ asmlinkage void segment_not_present(void);
>  asmlinkage void stack_segment(void);
>  asmlinkage void general_protection(void);
>  asmlinkage void page_fault(void);
> +asmlinkage void async_page_fault(void);
>  asmlinkage void spurious_interrupt_bug(void);
>  asmlinkage void coprocessor_error(void);
>  asmlinkage void alignment_check(void);
> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> index 227d009..e6e7273 100644
> --- a/arch/x86/kernel/entry_32.S
> +++ b/arch/x86/kernel/entry_32.S
> @@ -1496,6 +1496,16 @@ ENTRY(general_protection)
>  	CFI_ENDPROC
>  END(general_protection)
>  
> +#ifdef CONFIG_KVM_GUEST
> +ENTRY(async_page_fault)
> +	RING0_EC_FRAME
> +	pushl $do_async_page_fault
> +	CFI_ADJUST_CFA_OFFSET 4
> +	jmp error_code
> +	CFI_ENDPROC
> +END(apf_page_fault)
> +#endif
> +
>  /*
>   * End of kprobes section
>   */
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 17be5ec..def98c3 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -1349,6 +1349,9 @@ errorentry xen_stack_segment do_stack_segment
>  #endif
>  errorentry general_protection do_general_protection
>  errorentry page_fault do_page_fault
> +#ifdef CONFIG_KVM_GUEST
> +errorentry async_page_fault do_async_page_fault
> +#endif
>  #ifdef CONFIG_X86_MCE
>  paranoidzeroentry machine_check *machine_check_vector(%rip)
>  #endif
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 032d03b..d564063 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -29,8 +29,14 @@
>  #include <linux/hardirq.h>
>  #include <linux/notifier.h>
>  #include <linux/reboot.h>
> +#include <linux/hash.h>
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +#include <linux/kprobes.h>
>  #include <asm/timer.h>
>  #include <asm/cpu.h>
> +#include <asm/traps.h>
> +#include <asm/desc.h>
>  
>  #define MMU_QUEUE_SIZE 1024
>  
> @@ -64,6 +70,168 @@ static void kvm_io_delay(void)
>  {
>  }
>  
> +#define KVM_TASK_SLEEP_HASHBITS 8
> +#define KVM_TASK_SLEEP_HASHSIZE (1<<KVM_TASK_SLEEP_HASHBITS)
> +
> +struct kvm_task_sleep_node {
> +	struct hlist_node link;
> +	wait_queue_head_t wq;
> +	u32 token;
> +	int cpu;
> +};
> +
> +static struct kvm_task_sleep_head {
> +	spinlock_t lock;
> +	struct hlist_head list;
> +} async_pf_sleepers[KVM_TASK_SLEEP_HASHSIZE];
> +
> +static struct kvm_task_sleep_node *_find_apf_task(struct kvm_task_sleep_head *b,
> +						  u32 token)
> +{
> +	struct hlist_node *p;
> +
> +	hlist_for_each(p, &b->list) {
> +		struct kvm_task_sleep_node *n =
> +			hlist_entry(p, typeof(*n), link);
> +		if (n->token == token)
> +			return n;
> +	}
> +
> +	return NULL;
> +}
> +
> +void kvm_async_pf_task_wait(u32 token)
> +{
> +	u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
> +	struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
> +	struct kvm_task_sleep_node n, *e;
> +	DEFINE_WAIT(wait);
> +
> +	spin_lock(&b->lock);
> +	e = _find_apf_task(b, token);
> +	if (e) {
> +		/* dummy entry exist -> wake up was delivered ahead of PF */
> +		hlist_del(&e->link);
> +		kfree(e);
> +		spin_unlock(&b->lock);
> +		return;
> +	}
> +
> +	n.token = token;
> +	n.cpu = smp_processor_id();
> +	init_waitqueue_head(&n.wq);
> +	hlist_add_head(&n.link, &b->list);
> +	spin_unlock(&b->lock);
> +
> +	for (;;) {
> +		prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
> +		if (hlist_unhashed(&n.link))
> +			break;
> +		local_irq_enable();
> +		schedule();
> +		local_irq_disable();
> +	}
> +	finish_wait(&n.wq, &wait);
> +
> +	return;
> +}
> +EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
> +
> +static void apf_task_wake_one(struct kvm_task_sleep_node *n)
> +{
> +	hlist_del_init(&n->link);
> +	if (waitqueue_active(&n->wq))
> +		wake_up(&n->wq);
> +}
> +
> +static void apf_task_wake_all(void)
> +{
> +	int i;
> +
> +	for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) {
> +		struct hlist_node *p, *next;
> +		struct kvm_task_sleep_head *b = &async_pf_sleepers[i];
> +		spin_lock(&b->lock);
> +		hlist_for_each_safe(p, next, &b->list) {
> +			struct kvm_task_sleep_node *n =
> +				hlist_entry(p, typeof(*n), link);
> +			if (n->cpu == smp_processor_id())
> +				apf_task_wake_one(n);
> +		}
> +		spin_unlock(&b->lock);
> +	}
> +}
> +
> +void kvm_async_pf_task_wake(u32 token)
> +{
> +	u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
> +	struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
> +	struct kvm_task_sleep_node *n;
> +
> +	if (token == ~0) {
> +		apf_task_wake_all();
> +		return;
> +	}
> +
> +again:
> +	spin_lock(&b->lock);
> +	n = _find_apf_task(b, token);
> +	if (!n) {
> +		/*
> +		 * async PF was not yet handled.
> +		 * Add dummy entry for the token.
> +		 */
> +		n = kmalloc(sizeof(*n), GFP_ATOMIC);
> +		if (!n) {
> +			/*
> +			 * Allocation failed! Busy wait while other cpu
> +			 * handles async PF.
> +			 */
> +			spin_unlock(&b->lock);
> +			cpu_relax();
> +			goto again;
> +		}
> +		n->token = token;
> +		n->cpu = smp_processor_id();
> +		init_waitqueue_head(&n->wq);
> +		hlist_add_head(&n->link, &b->list);
> +	} else
> +		apf_task_wake_one(n);
> +	spin_unlock(&b->lock);
> +	return;
> +}
> +EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);
> +
> +u32 kvm_read_and_reset_pf_reason(void)
> +{
> +	u32 reason = 0;
> +
> +	if (__get_cpu_var(apf_reason).enabled) {
> +		reason = __get_cpu_var(apf_reason).reason;
> +		__get_cpu_var(apf_reason).reason = 0;
> +	}
> +
> +	return reason;
> +}
> +EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason);
> +
> +dotraplinkage void __kprobes
> +do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
> +{
> +	switch (kvm_read_and_reset_pf_reason()) {
> +	default:
> +		do_page_fault(regs, error_code);
> +		break;
> +	case KVM_PV_REASON_PAGE_NOT_PRESENT:
> +		/* page is swapped out by the host. */
> +		kvm_async_pf_task_wait((u32)read_cr2());
> +		break;
> +	case KVM_PV_REASON_PAGE_READY:
> +		kvm_async_pf_task_wake((u32)read_cr2());
> +		break;
> +	}
> +}
> +
>  static void kvm_mmu_op(void *buffer, unsigned len)
>  {
>  	int r;
> @@ -300,6 +468,7 @@ static void kvm_guest_cpu_online(void *dummy)
>  static void kvm_guest_cpu_offline(void *dummy)
>  {
>  	kvm_pv_disable_apf(NULL);
> +	apf_task_wake_all();
>  }
>  
>  static int __cpuinit kvm_cpu_notify(struct notifier_block *self,
> @@ -327,13 +496,25 @@ static struct notifier_block __cpuinitdata kvm_cpu_notifier = {
>  };
>  #endif
>  
> +static void __init kvm_apf_trap_init(void)
> +{
> +	set_intr_gate(14, &async_page_fault);
> +}
> +
>  void __init kvm_guest_init(void)
>  {
> +	int i;
> +
>  	if (!kvm_para_available())
>  		return;
>  
>  	paravirt_ops_setup();
>  	register_reboot_notifier(&kvm_pv_reboot_nb);
> +	for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
> +		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;
> +
>  #ifdef CONFIG_SMP
>  	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
>  	register_cpu_notifier(&kvm_cpu_notifier);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 9a92224..9fa27a5 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -31,6 +31,7 @@
>  
>  #include <asm/tlbflush.h>
>  #include <asm/desc.h>
> +#include <asm/kvm_para.h>
>  
>  #include <asm/virtext.h>
>  #include "trace.h"
> @@ -133,6 +134,7 @@ struct vcpu_svm {
>  
>  	unsigned int3_injected;
>  	unsigned long int3_rip;
> +	u32 apf_reason;
>  };
>  
>  #define MSR_INVALID			0xffffffffU
> @@ -1383,16 +1385,33 @@ static void svm_set_dr7(struct kvm_vcpu *vcpu, unsigned long value)
>  
>  static int pf_interception(struct vcpu_svm *svm)
>  {
> -	u64 fault_address;
> +	u64 fault_address = svm->vmcb->control.exit_info_2;
>  	u32 error_code;
> +	int r = 1;
>  
> -	fault_address  = svm->vmcb->control.exit_info_2;
> -	error_code = svm->vmcb->control.exit_info_1;
> +	switch (svm->apf_reason) {
> +	default:
> +		error_code = svm->vmcb->control.exit_info_1;
>  
> -	trace_kvm_page_fault(fault_address, error_code);
> -	if (!npt_enabled && kvm_event_needs_reinjection(&svm->vcpu))
> -		kvm_mmu_unprotect_page_virt(&svm->vcpu, fault_address);
> -	return kvm_mmu_page_fault(&svm->vcpu, fault_address, error_code);
> +		trace_kvm_page_fault(fault_address, error_code);
> +		if (!npt_enabled && kvm_event_needs_reinjection(&svm->vcpu))
> +			kvm_mmu_unprotect_page_virt(&svm->vcpu, fault_address);
> +		r = kvm_mmu_page_fault(&svm->vcpu, fault_address, error_code);
> +		break;
> +	case KVM_PV_REASON_PAGE_NOT_PRESENT:
> +		svm->apf_reason = 0;
> +		local_irq_disable();
> +		kvm_async_pf_task_wait(fault_address);
> +		local_irq_enable();
> +		break;
> +	case KVM_PV_REASON_PAGE_READY:
> +		svm->apf_reason = 0;
> +		local_irq_disable();
> +		kvm_async_pf_task_wake(fault_address);
> +		local_irq_enable();
> +		break;

That's only available if CONFIG_KVM_GUEST is set, no? Is there anything
I miss that resolves this dependency automatically? Otherwise, some more
#ifdef CONFIG_KVM_GUEST might be needed.

Jan

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