[RFC,v8,2/7] KVM: Enabling guest free page hinting via static key
diff mbox series

Message ID 20190204201854.2328-3-nitesh@redhat.com
State New
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Series
  • KVM: Guest Free Page Hinting
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Commit Message

Nitesh Narayan Lal Feb. 4, 2019, 8:18 p.m. UTC
This patch enables the guest free page hinting support
to enable or disable based on the STATIC key which
could be set via sysctl.

Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
---
 include/linux/gfp.h          |  2 ++
 include/linux/page_hinting.h |  5 +++++
 kernel/sysctl.c              |  9 +++++++++
 virt/kvm/page_hinting.c      | 23 +++++++++++++++++++++++
 4 files changed, 39 insertions(+)

Comments

Alexander Duyck Feb. 8, 2019, 6:07 p.m. UTC | #1
On Mon, Feb 4, 2019 at 2:11 PM Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>
> This patch enables the guest free page hinting support
> to enable or disable based on the STATIC key which
> could be set via sysctl.
>
> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
> ---
>  include/linux/gfp.h          |  2 ++
>  include/linux/page_hinting.h |  5 +++++
>  kernel/sysctl.c              |  9 +++++++++
>  virt/kvm/page_hinting.c      | 23 +++++++++++++++++++++++
>  4 files changed, 39 insertions(+)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index e596527284ba..8389219a076a 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -461,6 +461,8 @@ static inline struct zonelist *node_zonelist(int nid, gfp_t flags)
>  #define HAVE_ARCH_FREE_PAGE
>  static inline void arch_free_page(struct page *page, int order)
>  {
> +       if (!static_branch_unlikely(&guest_page_hinting_key))
> +               return;
>         guest_free_page(page, order);
>  }
>  #endif
> diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h
> index b54f7428f348..9bdcf63e1306 100644
> --- a/include/linux/page_hinting.h
> +++ b/include/linux/page_hinting.h
> @@ -14,4 +14,9 @@ struct hypervisor_pages {
>         unsigned int order;
>  };
>
> +extern int guest_page_hinting_flag;
> +extern struct static_key_false guest_page_hinting_key;
> +
> +int guest_page_hinting_sysctl(struct ctl_table *table, int write,
> +                             void __user *buffer, size_t *lenp, loff_t *ppos);
>  void guest_free_page(struct page *page, int order);
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index ba4d9e85feb8..5d53629c9bfb 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1690,6 +1690,15 @@ static struct ctl_table vm_table[] = {
>                 .extra1         = (void *)&mmap_rnd_compat_bits_min,
>                 .extra2         = (void *)&mmap_rnd_compat_bits_max,
>         },
> +#endif
> +#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
>         { }
>  };

Since you are adding a new sysctl shouldn't you also be updating
Documentation/sysctl/vm.txt?

> diff --git a/virt/kvm/page_hinting.c b/virt/kvm/page_hinting.c
> index 818bd6b84e0c..4a34ea8db0c8 100644
> --- a/virt/kvm/page_hinting.c
> +++ b/virt/kvm/page_hinting.c
> @@ -1,6 +1,7 @@
>  #include <linux/gfp.h>
>  #include <linux/mm.h>
>  #include <linux/kernel.h>
> +#include <linux/kvm_host.h>
>
>  /*
>   * struct kvm_free_pages - Tracks the pages which are freed by the guest.
> @@ -31,6 +32,28 @@ struct page_hinting {
>
>  DEFINE_PER_CPU(struct page_hinting, hinting_obj);
>
> +struct static_key_false guest_page_hinting_key  = STATIC_KEY_FALSE_INIT;
> +EXPORT_SYMBOL(guest_page_hinting_key);
> +static DEFINE_MUTEX(hinting_mutex);
> +int guest_page_hinting_flag;
> +EXPORT_SYMBOL(guest_page_hinting_flag);

I'm not entirely sure this flag makes sense to me. What is to prevent
someone from turning this on when there is no means of actually using
the hints. I understand right now that guest_free_page doesn't
actually do anything, but when it does I would assume it has to
interact with a device. If that device is not present would it still
make sense for us to be generating hints?

> +
> +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;
> +}
> +
>  void guest_free_page(struct page *page, int order)
>  {
>  }
> --
> 2.17.2
>
Nitesh Narayan Lal Feb. 8, 2019, 6:22 p.m. UTC | #2
On 2/8/19 1:07 PM, Alexander Duyck wrote:
> On Mon, Feb 4, 2019 at 2:11 PM Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>> This patch enables the guest free page hinting support
>> to enable or disable based on the STATIC key which
>> could be set via sysctl.
>>
>> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
>> ---
>>  include/linux/gfp.h          |  2 ++
>>  include/linux/page_hinting.h |  5 +++++
>>  kernel/sysctl.c              |  9 +++++++++
>>  virt/kvm/page_hinting.c      | 23 +++++++++++++++++++++++
>>  4 files changed, 39 insertions(+)
>>
>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
>> index e596527284ba..8389219a076a 100644
>> --- a/include/linux/gfp.h
>> +++ b/include/linux/gfp.h
>> @@ -461,6 +461,8 @@ static inline struct zonelist *node_zonelist(int nid, gfp_t flags)
>>  #define HAVE_ARCH_FREE_PAGE
>>  static inline void arch_free_page(struct page *page, int order)
>>  {
>> +       if (!static_branch_unlikely(&guest_page_hinting_key))
>> +               return;
>>         guest_free_page(page, order);
>>  }
>>  #endif
>> diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h
>> index b54f7428f348..9bdcf63e1306 100644
>> --- a/include/linux/page_hinting.h
>> +++ b/include/linux/page_hinting.h
>> @@ -14,4 +14,9 @@ struct hypervisor_pages {
>>         unsigned int order;
>>  };
>>
>> +extern int guest_page_hinting_flag;
>> +extern struct static_key_false guest_page_hinting_key;
>> +
>> +int guest_page_hinting_sysctl(struct ctl_table *table, int write,
>> +                             void __user *buffer, size_t *lenp, loff_t *ppos);
>>  void guest_free_page(struct page *page, int order);
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index ba4d9e85feb8..5d53629c9bfb 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -1690,6 +1690,15 @@ static struct ctl_table vm_table[] = {
>>                 .extra1         = (void *)&mmap_rnd_compat_bits_min,
>>                 .extra2         = (void *)&mmap_rnd_compat_bits_max,
>>         },
>> +#endif
>> +#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
>>         { }
>>  };
> Since you are adding a new sysctl shouldn't you also be updating
> Documentation/sysctl/vm.txt?
Indeed I will be doing that.
However, I would first like to close other major issues with the design.
>
>> diff --git a/virt/kvm/page_hinting.c b/virt/kvm/page_hinting.c
>> index 818bd6b84e0c..4a34ea8db0c8 100644
>> --- a/virt/kvm/page_hinting.c
>> +++ b/virt/kvm/page_hinting.c
>> @@ -1,6 +1,7 @@
>>  #include <linux/gfp.h>
>>  #include <linux/mm.h>
>>  #include <linux/kernel.h>
>> +#include <linux/kvm_host.h>
>>
>>  /*
>>   * struct kvm_free_pages - Tracks the pages which are freed by the guest.
>> @@ -31,6 +32,28 @@ struct page_hinting {
>>
>>  DEFINE_PER_CPU(struct page_hinting, hinting_obj);
>>
>> +struct static_key_false guest_page_hinting_key  = STATIC_KEY_FALSE_INIT;
>> +EXPORT_SYMBOL(guest_page_hinting_key);
>> +static DEFINE_MUTEX(hinting_mutex);
>> +int guest_page_hinting_flag;
>> +EXPORT_SYMBOL(guest_page_hinting_flag);
> I'm not entirely sure this flag makes sense to me. What is to prevent
> someone from turning this on when there is no means of actually using
> the hints. I understand right now that guest_free_page doesn't
> actually do anything, but when it does I would assume it has to
> interact with a device. If that device is not present would it still
> make sense for us to be generating hints?
Fair point, I will address this issue.
>
>> +
>> +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;
>> +}
>> +
>>  void guest_free_page(struct page *page, int order)
>>  {
>>  }
>> --
>> 2.17.2
>>

Patch
diff mbox series

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index e596527284ba..8389219a076a 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -461,6 +461,8 @@  static inline struct zonelist *node_zonelist(int nid, gfp_t flags)
 #define HAVE_ARCH_FREE_PAGE
 static inline void arch_free_page(struct page *page, int order)
 {
+	if (!static_branch_unlikely(&guest_page_hinting_key))
+		return;
 	guest_free_page(page, order);
 }
 #endif
diff --git a/include/linux/page_hinting.h b/include/linux/page_hinting.h
index b54f7428f348..9bdcf63e1306 100644
--- a/include/linux/page_hinting.h
+++ b/include/linux/page_hinting.h
@@ -14,4 +14,9 @@  struct hypervisor_pages {
 	unsigned int order;
 };
 
+extern int guest_page_hinting_flag;
+extern struct static_key_false guest_page_hinting_key;
+
+int guest_page_hinting_sysctl(struct ctl_table *table, int write,
+			      void __user *buffer, size_t *lenp, loff_t *ppos);
 void guest_free_page(struct page *page, int order);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ba4d9e85feb8..5d53629c9bfb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1690,6 +1690,15 @@  static struct ctl_table vm_table[] = {
 		.extra1		= (void *)&mmap_rnd_compat_bits_min,
 		.extra2		= (void *)&mmap_rnd_compat_bits_max,
 	},
+#endif
+#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 818bd6b84e0c..4a34ea8db0c8 100644
--- a/virt/kvm/page_hinting.c
+++ b/virt/kvm/page_hinting.c
@@ -1,6 +1,7 @@ 
 #include <linux/gfp.h>
 #include <linux/mm.h>
 #include <linux/kernel.h>
+#include <linux/kvm_host.h>
 
 /*
  * struct kvm_free_pages - Tracks the pages which are freed by the guest.
@@ -31,6 +32,28 @@  struct page_hinting {
 
 DEFINE_PER_CPU(struct page_hinting, hinting_obj);
 
+struct static_key_false guest_page_hinting_key  = STATIC_KEY_FALSE_INIT;
+EXPORT_SYMBOL(guest_page_hinting_key);
+static DEFINE_MUTEX(hinting_mutex);
+int guest_page_hinting_flag;
+EXPORT_SYMBOL(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;
+}
+
 void guest_free_page(struct page *page, int order)
 {
 }