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.
Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_para.h | 3 +
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 | 170 +++++++++++++++++++++++++++++++++++++++
5 files changed, 187 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index f1662d7..edf07cf 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;
__u32 enabled;
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 cd49141..95e13da 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1494,6 +1494,16 @@ 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 0697ff1..65c3eb6 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1346,6 +1346,9 @@ 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 be1966a..fa9f520 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
@@ -54,6 +60,158 @@ 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,
+ u64 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;
+}
+
+static void apf_task_wait(struct task_struct *tsk, 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;
+ schedule();
+ }
+ finish_wait(&n.wq, &wait);
+
+ return;
+}
+
+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(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;
+
+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 vcpu
+ * 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;
+}
+
+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);
+ }
+}
+
+dotraplinkage void __kprobes
+do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
+{
+ u32 reason = 0, token;
+
+ if (__get_cpu_var(apf_reason).enabled) {
+ reason = __get_cpu_var(apf_reason).reason;
+ __get_cpu_var(apf_reason).reason = 0;
+
+ token = (u32)read_cr2();
+ }
+
+ switch (reason) {
+ default:
+ do_page_fault(regs, error_code);
+ break;
+ case KVM_PV_REASON_PAGE_NOT_PRESENT:
+ /* page is swapped out by the host. */
+ apf_task_wait(current, token);
+ break;
+ case KVM_PV_REASON_PAGE_READY:
+ if (unlikely(token == ~0))
+ apf_task_wake_all();
+ else
+ apf_task_wake(token);
+ break;
+ }
+}
+
static void kvm_mmu_op(void *buffer, unsigned len)
{
int r;
@@ -268,13 +426,25 @@ static void __init kvm_smp_prepare_boot_cpu(void)
}
#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;
#else
--
1.7.1
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