[Patch v4 6/6] KVM: Enabling guest page hinting via static key

[nilal@redhat.com]

From: Nitesh Narayan Lal <nilal@redhat.com>

This patch adds the support for enabling or disabling
the guest page hinting based on the STATIC key which
could be set via sysctl.

Signed-off-by: Nitesh Narayan Lal <nilal@redhat.com>
---
 include/linux/page_hinting.h |  3 +++
 kernel/sysctl.c              | 10 ++++++++++
 virt/kvm/page_hinting.c      | 26 ++++++++++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h
index 0bfb646..6f6068a 100644
--- a/include/linux/page_hinting.h
+++ b/include/linux/page_hinting.h
@@ -14,3 +14,6 @@ struct hypervisor_pages {
 extern struct hypervisor_pages hypervisor_pagelist[MAX_FGPT_ENTRIES];
 extern void (*request_hypercall)(void *, int);
 extern void *balloon_ptr;
+int guest_page_hinting_sysctl(struct ctl_table *table, int write,
+			      void __user *buffer, size_t *lenp, loff_t *ppos);
+extern int guest_page_hinting_flag;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index d9c31bc..f4c4ddc 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -67,6 +67,7 @@
 #include <linux/kexec.h>
 #include <linux/bpf.h>
 #include <linux/mount.h>
+#include <linux/page_hinting.h>
 
 #include <linux/uaccess.h>
 #include <asm/processor.h>
@@ -1849,6 +1850,15 @@ static struct ctl_table fs_table[] = {
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &one,
 	},
+#ifdef CONFIG_KVM_FREE_PAGE_HINTING
+	{
+		.procname	= "guest-page-hinting",
+		.data		= &guest_page_hinting_flag,
+		.maxlen		= sizeof(guest_page_hinting_flag),
+		.mode		= 0644,
+		.proc_handler   = guest_page_hinting_sysctl,
+	},
+#endif
 	{ }
 };
 
diff --git a/virt/kvm/page_hinting.c b/virt/kvm/page_hinting.c
index 22c892b..d4bfbce 100644
--- a/virt/kvm/page_hinting.c
+++ b/virt/kvm/page_hinting.c
@@ -30,6 +30,28 @@ void (*request_hypercall)(void *, int);
 EXPORT_SYMBOL(request_hypercall);
 void *balloon_ptr;
 EXPORT_SYMBOL(balloon_ptr);
+DEFINE_STATIC_KEY_FALSE(guest_page_hinting_key);
+EXPORT_SYMBOL(guest_page_hinting_key);
+static DEFINE_MUTEX(hinting_mutex);
+int guest_page_hinting_flag;
+
+int guest_page_hinting_sysctl(struct ctl_table *table, int write,
+			      void __user *buffer, size_t *lenp,
+			      loff_t *ppos)
+{
+	int ret;
+
+	mutex_lock(&hinting_mutex);
+
+	ret = proc_dointvec(table, write, buffer, lenp, ppos);
+
+	if (guest_page_hinting_flag)
+		static_key_enable(&guest_page_hinting_key.key);
+	else
+		static_key_disable(&guest_page_hinting_key.key);
+	mutex_unlock(&hinting_mutex);
+	return ret;
+}
 
 static void empty_hyperlist(void)
 {
@@ -258,6 +280,8 @@ void arch_alloc_page(struct page *page, int order)
 {
 	unsigned int seq;
 
+	if (!static_branch_unlikely(&guest_page_hinting_key))
+		return;
 	/*
 	 * arch_free_page will acquire the lock once the list carrying guest
 	 * free pages is full and a hypercall will be made. Until complete free
@@ -276,6 +300,8 @@ void arch_free_page(struct page *page, int order)
 	struct kvm_free_pages *free_page_obj;
 	unsigned long flags;
 
+	if (!static_branch_unlikely(&guest_page_hinting_key))
+		return;
 	/*
 	 * use of global variables may trigger a race condition between irq and
 	 * process context causing unwanted overwrites. This will be replaced
-- 
2.9.4