Wait queues, allowing conditional sleep in hypervisor context.

Signed-off-by: Keir Fraser <keir@xen.org>

1 files changed, 165 insertions, 0 deletions

diff --git a/xen/common/wait.c b/xen/common/wait.c
new file mode 100644
index 0000000000..cb63f85916
--- /dev/null
+++ b/xen/common/wait.c
@@ -0,0 +1,165 @@
+/******************************************************************************
+ * wait.c
+ * 
+ * Sleep in hypervisor context for some event to occur.
+ */
+
+#include <xen/config.h>
+#include <xen/sched.h>
+#include <xen/wait.h>
+
+struct waitqueue_vcpu {
+    struct list_head list;
+    struct vcpu *vcpu;
+#ifdef CONFIG_X86
+    /*
+     * Xen/x86 does not have per-vcpu hypervisor stacks. So we must save the
+     * hypervisor context before sleeping (descheduling), setjmp/longjmp-style.
+     */
+    void *esp;
+    char stack[1500];
+#endif
+};
+
+int init_waitqueue_vcpu(struct vcpu *v)
+{
+    struct waitqueue_vcpu *wqv;
+
+    wqv = xmalloc(struct waitqueue_vcpu);
+    if ( wqv == NULL )
+        return -ENOMEM;
+
+    memset(wqv, 0, sizeof(*wqv));
+    INIT_LIST_HEAD(&wqv->list);
+    wqv->vcpu = v;
+
+    v->waitqueue_vcpu = wqv;
+
+    return 0;
+}
+
+void destroy_waitqueue_vcpu(struct vcpu *v)
+{
+    struct waitqueue_vcpu *wqv;
+
+    wqv = v->waitqueue_vcpu;
+    if ( wqv == NULL )
+        return;
+
+    BUG_ON(!list_empty(&wqv->list));
+    xfree(wqv);
+
+    v->waitqueue_vcpu = NULL;
+}
+
+void init_waitqueue_head(struct waitqueue_head *wq)
+{
+    spin_lock_init(&wq->lock);
+    INIT_LIST_HEAD(&wq->list);
+}
+
+void wake_up(struct waitqueue_head *wq)
+{
+    struct waitqueue_vcpu *wqv;
+
+    spin_lock(&wq->lock);
+
+    while ( !list_empty(&wq->list) )
+    {
+        wqv = list_entry(wq->list.next, struct waitqueue_vcpu, list);
+        list_del_init(&wqv->list);
+        vcpu_unpause(wqv->vcpu);
+    }
+
+    spin_unlock(&wq->lock);
+}
+
+#ifdef CONFIG_X86
+
+static void __prepare_to_wait(struct waitqueue_vcpu *wqv)
+{
+    char *cpu_info = (char *)get_cpu_info();
+    asm volatile (
+#ifdef CONFIG_X86_64
+        "push %%rax; push %%rbx; push %%rcx; push %%rdx; push %%rdi; "
+        "push %%rbp; push %%r8; push %%r9; push %%r10; push %%r11; "
+        "push %%r12; push %%r13; push %%r14; push %%r15; call 1f; "
+        "1: mov 80(%%rsp),%%rdi; mov 96(%%rsp),%%rcx; mov %%rsp,%%rsi; "
+        "sub %%rsi,%%rcx; rep movsb; mov %%rsp,%%rsi; pop %%rax; "
+        "pop %%r15; pop %%r14; pop %%r13; pop %%r12; "
+        "pop %%r11; pop %%r10; pop %%r9; pop %%r8; "
+        "pop %%rbp; pop %%rdi; pop %%rdx; pop %%rcx; pop %%rbx; pop %%rax"
+#else
+        "push %%eax; push %%ebx; push %%ecx; push %%edx; push %%edi; "
+        "push %%ebp; call 1f; "
+        "1: mov 8(%%esp),%%edi; mov 16(%%esp),%%ecx; mov %%esp,%%esi; "
+        "sub %%esi,%%ecx; rep movsb; mov %%esp,%%esi; pop %%eax; "
+        "pop %%ebp; pop %%edi; pop %%edx; pop %%ecx; pop %%ebx; pop %%eax"
+#endif
+        : "=S" (wqv->esp)
+        : "c" (cpu_info), "D" (wqv->stack)
+        : "memory" );
+    BUG_ON((cpu_info - (char *)wqv->esp) > sizeof(wqv->stack));
+}
+
+static void __finish_wait(struct waitqueue_vcpu *wqv)
+{
+    wqv->esp = NULL;
+}
+
+void check_wakeup_from_wait(void)
+{
+    struct waitqueue_vcpu *wqv = current->waitqueue_vcpu;
+
+    ASSERT(list_empty(&wqv->list));
+
+    if ( likely(wqv->esp == NULL) )
+        return;
+
+    asm volatile (
+        "mov %1,%%"__OP"sp; rep movsb; jmp *(%%"__OP"sp)"
+        : : "S" (wqv->stack), "D" (wqv->esp),
+        "c" ((char *)get_cpu_info() - (char *)wqv->esp)
+        : "memory" );
+}
+
+#else /* !CONFIG_X86 */
+
+#define __prepare_to_wait(wqv) ((void)0)
+#define __finish_wait(wqv) ((void)0)
+
+#endif
+
+void prepare_to_wait(struct waitqueue_head *wq)
+{
+    struct vcpu *curr = current;
+    struct waitqueue_vcpu *wqv = curr->waitqueue_vcpu;
+
+    ASSERT(list_empty(&wqv->list));
+
+    spin_lock(&wq->lock);
+    list_add_tail(&wqv->list, &wq->list);
+    vcpu_pause_nosync(curr);
+    spin_unlock(&wq->lock);
+
+    __prepare_to_wait(wqv);
+}
+
+void finish_wait(struct waitqueue_head *wq)
+{
+    struct vcpu *curr = current;
+    struct waitqueue_vcpu *wqv = curr->waitqueue_vcpu;
+
+    __finish_wait(wqv);
+
+    if ( list_empty(&wqv->list) )
+        return;
+
+    spin_lock(&wq->lock);
+    if ( !list_empty(&wqv->list) )
+    {
+        list_del_init(&wqv->list);
+        vcpu_unpause(curr);
+    }
+    spin_unlock(&wq->lock);
+}