On Mon, Feb 4, 2019 at 2:11 PM Nitesh Narayan Lal <nitesh@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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
>
