Re: [PATCH v8 05/15] x86/sgx: Add sgx_epc_lru_list to encapsulate LRU list

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Tue Jan 30, 2024 at 4:09 AM EET, Haitao Huang wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Introduce a data structure to wrap the existing reclaimable list and its
> spinlock. Each cgroup later will have one instance of this structure to
> track EPC pages allocated for processes associated with the same cgroup.
> Just like the global SGX reclaimer (ksgxd), an EPC cgroup reclaims pages
> from the reclaimable list in this structure when its usage reaches near
> its limit.
>
> Use this structure to encapsulate the LRU list and its lock used by the
> global reclaimer.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Co-developed-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> Co-developed-by: Haitao Huang <haitao.huang@linux.intel.com>
> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>

I'd put author as last sob but that said I'm not sure if there is rigid
rule to do so. Thus not saying must here.

> Cc: Sean Christopherson <seanjc@google.com>
> ---
> V6:
> - removed introduction to unreclaimables in commit message.
>
> V4:
> - Removed unneeded comments for the spinlock and the non-reclaimables.
> (Kai, Jarkko)
> - Revised the commit to add introduction comments for unreclaimables and
> multiple LRU lists.(Kai)
> - Reordered the patches: delay all changes for unreclaimables to
> later, and this one becomes the first change in the SGX subsystem.
>
> V3:
> - Removed the helper functions and revised commit messages.
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 39 +++++++++++++++++-----------------
>  arch/x86/kernel/cpu/sgx/sgx.h  | 15 +++++++++++++
>  2 files changed, 35 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index c32f18b70c73..912959c7ecc9 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -28,10 +28,9 @@ static DEFINE_XARRAY(sgx_epc_address_space);
>  
>  /*
>   * These variables are part of the state of the reclaimer, and must be accessed
> - * with sgx_reclaimer_lock acquired.
> + * with sgx_global_lru.lock acquired.
>   */
> -static LIST_HEAD(sgx_active_page_list);
> -static DEFINE_SPINLOCK(sgx_reclaimer_lock);
> +static struct sgx_epc_lru_list sgx_global_lru;
>  
>  static atomic_long_t sgx_nr_free_pages = ATOMIC_LONG_INIT(0);
>  
> @@ -306,13 +305,13 @@ static void sgx_reclaim_pages(void)
>  	int ret;
>  	int i;
>  
> -	spin_lock(&sgx_reclaimer_lock);
> +	spin_lock(&sgx_global_lru.lock);
>  	for (i = 0; i < SGX_NR_TO_SCAN; i++) {
> -		if (list_empty(&sgx_active_page_list))
> +		epc_page = list_first_entry_or_null(&sgx_global_lru.reclaimable,
> +						    struct sgx_epc_page, list);
> +		if (!epc_page)
>  			break;
>  
> -		epc_page = list_first_entry(&sgx_active_page_list,
> -					    struct sgx_epc_page, list);
>  		list_del_init(&epc_page->list);
>  		encl_page = epc_page->owner;
>  
> @@ -324,7 +323,7 @@ static void sgx_reclaim_pages(void)
>  			 */
>  			epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
>  	}
> -	spin_unlock(&sgx_reclaimer_lock);
> +	spin_unlock(&sgx_global_lru.lock);
>  
>  	for (i = 0; i < cnt; i++) {
>  		epc_page = chunk[i];
> @@ -347,9 +346,9 @@ static void sgx_reclaim_pages(void)
>  		continue;
>  
>  skip:
> -		spin_lock(&sgx_reclaimer_lock);
> -		list_add_tail(&epc_page->list, &sgx_active_page_list);
> -		spin_unlock(&sgx_reclaimer_lock);
> +		spin_lock(&sgx_global_lru.lock);
> +		list_add_tail(&epc_page->list, &sgx_global_lru.reclaimable);
> +		spin_unlock(&sgx_global_lru.lock);
>  
>  		kref_put(&encl_page->encl->refcount, sgx_encl_release);
>  
> @@ -380,7 +379,7 @@ static void sgx_reclaim_pages(void)
>  static bool sgx_should_reclaim(unsigned long watermark)
>  {
>  	return atomic_long_read(&sgx_nr_free_pages) < watermark &&
> -	       !list_empty(&sgx_active_page_list);
> +	       !list_empty(&sgx_global_lru.reclaimable);
>  }
>  
>  /*
> @@ -432,6 +431,8 @@ static bool __init sgx_page_reclaimer_init(void)
>  
>  	ksgxd_tsk = tsk;
>  
> +	sgx_lru_init(&sgx_global_lru);
> +
>  	return true;
>  }
>  
> @@ -507,10 +508,10 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
>   */
>  void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
>  {
> -	spin_lock(&sgx_reclaimer_lock);
> +	spin_lock(&sgx_global_lru.lock);
>  	page->flags |= SGX_EPC_PAGE_RECLAIMER_TRACKED;
> -	list_add_tail(&page->list, &sgx_active_page_list);
> -	spin_unlock(&sgx_reclaimer_lock);
> +	list_add_tail(&page->list, &sgx_global_lru.reclaimable);
> +	spin_unlock(&sgx_global_lru.lock);
>  }
>  
>  /**
> @@ -525,18 +526,18 @@ void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
>   */
>  int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
>  {
> -	spin_lock(&sgx_reclaimer_lock);
> +	spin_lock(&sgx_global_lru.lock);
>  	if (page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED) {
>  		/* The page is being reclaimed. */
>  		if (list_empty(&page->list)) {
> -			spin_unlock(&sgx_reclaimer_lock);
> +			spin_unlock(&sgx_global_lru.lock);
>  			return -EBUSY;
>  		}
>  
>  		list_del(&page->list);
>  		page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
>  	}
> -	spin_unlock(&sgx_reclaimer_lock);
> +	spin_unlock(&sgx_global_lru.lock);
>  
>  	return 0;
>  }
> @@ -578,7 +579,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
>  			break;
>  		}
>  
> -		if (list_empty(&sgx_active_page_list)) {
> +		if (list_empty(&sgx_global_lru.reclaimable)) {
>  			page = ERR_PTR(-ENOMEM);
>  			break;
>  		}
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index a898d86dead0..0e99e9ae3a67 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -88,6 +88,21 @@ static inline void *sgx_get_epc_virt_addr(struct sgx_epc_page *page)
>  	return section->virt_addr + index * PAGE_SIZE;
>  }
>  
> +/*
> + * Contains EPC pages tracked by the global reclaimer (ksgxd) or an EPC
> + * cgroup.
> + */
> +struct sgx_epc_lru_list {
> +	spinlock_t lock;
> +	struct list_head reclaimable;
> +};
> +
> +static inline void sgx_lru_init(struct sgx_epc_lru_list *lru)
> +{
> +	spin_lock_init(&lru->lock);
> +	INIT_LIST_HEAD(&lru->reclaimable);
> +}
> +
>  struct sgx_epc_page *__sgx_alloc_epc_page(void);
>  void sgx_free_epc_page(struct sgx_epc_page *page);
>  

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko