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

    --
    Siemens AG, Corporate Technology, CT T DE IT 1
    Corporate Competence Center Embedded Linux


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