[RFC][PATCH 1/5] [PATCH 1/5] kvm: register in task_struct

[Fengguang Wu]

The added pointer will be used by the /proc/PID/idle_bitmap code to
quickly identify QEMU task and walk EPT/NPT accordingly. For virtual
machines, the A bits will be set in guest page tables and EPT/NPT,
rather than the QEMU task page table.

This costs 8 bytes in task_struct which could be wasteful for the
majority normal tasks. The alternative is to add a flag only, and
let it find the corresponding VM in kvm vm_list.

Signed-off-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
---
 include/linux/sched.h | 10 ++++++++++
 virt/kvm/kvm_main.c   |  1 +
 2 files changed, 11 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 43731fe51c97..26c8549bbc28 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -38,6 +38,7 @@ struct cfs_rq;
 struct fs_struct;
 struct futex_pi_state;
 struct io_context;
+struct kvm;
 struct mempolicy;
 struct nameidata;
 struct nsproxy;
@@ -1179,6 +1180,9 @@ struct task_struct {
 	/* Used by LSM modules for access restriction: */
 	void				*security;
 #endif
+#if IS_ENABLED(CONFIG_KVM)
+        struct kvm                      *kvm;
+#endif
 
 	/*
 	 * New fields for task_struct should be added above here, so that
@@ -1898,4 +1902,10 @@ static inline void rseq_syscall(struct pt_regs *regs)
 
 #endif
 
+#if IS_ENABLED(CONFIG_KVM)
+static inline struct kvm *task_kvm(struct task_struct *t) { return t->kvm; }
+#else
+static inline struct kvm *task_kvm(struct task_struct *t) { return NULL; }
+#endif
+
 #endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8b47507faab5..0c483720de8d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3892,6 +3892,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
 	if (type == KVM_EVENT_CREATE_VM) {
 		add_uevent_var(env, "EVENT=create");
 		kvm->userspace_pid = task_pid_nr(current);
+		current->kvm = kvm;
 	} else if (type == KVM_EVENT_DESTROY_VM) {
 		add_uevent_var(env, "EVENT=destroy");
 	}
-- 
2.15.0