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

Jan Kiszka
2010-10-20T11:48:45Z

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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