Re: [RFC PATCH 04/20] x86/sgx: Add 'struct sgx_epc_lru' to encapsulate lru list(s)

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Sep 22, 2022 at 10:10:41AM -0700, Kristen Carlson Accardi wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
> 
> Wrap the existing reclaimable list and its spinlock in a struct to
> minimize the code changes needed to handle multiple LRUs as well as
> reclaimable and non-reclaimable lists, both of which will be introduced
> and used by SGX EPC cgroups.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> Cc: Sean Christopherson <seanjc@google.com>

The commit message could explicitly state the added data type.

The data type is not LRU: together with the LIFO list, i.e.
a queue, the code implements LRU alike policy.

I would name the data type as sgx_epc_queue because it is a 
less confusing name.

> ---
>  arch/x86/kernel/cpu/sgx/main.c | 37 +++++++++++++++++-----------------
>  arch/x86/kernel/cpu/sgx/sgx.h  | 11 ++++++++++
>  2 files changed, 30 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 4cdeb915dc86..af68dc1c677b 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -26,10 +26,9 @@ 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 sgx_global_lru;
>  
>  static atomic_long_t sgx_nr_free_pages = ATOMIC_LONG_INIT(0);
>  
> @@ -298,12 +297,12 @@ 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))
> +		if (list_empty(&sgx_global_lru.reclaimable))
>  			break;
>  
> -		epc_page = list_first_entry(&sgx_active_page_list,
> +		epc_page = list_first_entry(&sgx_global_lru.reclaimable,
>  					    struct sgx_epc_page, list);
>  		list_del_init(&epc_page->list);
>  		encl_page = epc_page->owner;
> @@ -316,7 +315,7 @@ 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];
> @@ -339,9 +338,9 @@ 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);
>  
> @@ -374,7 +373,7 @@ 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);
>  }
>  
>  /*
> @@ -427,6 +426,8 @@ static bool __init sgx_page_reclaimer_init(void)
>  
>  	ksgxd_tsk = tsk;
>  
> +	sgx_lru_init(&sgx_global_lru);
> +
>  	return true;
>  }
>  
> @@ -502,10 +503,10 @@ 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);
>  }
>  
>  /**
> @@ -520,18 +521,18 @@ 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;
>  }
> @@ -564,7 +565,7 @@ 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))
>  			return ERR_PTR(-ENOMEM);
>  
>  		if (!reclaim) {
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 5a7e858a8f98..7b208ee8eb45 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -83,6 +83,17 @@ static inline void *sgx_get_epc_virt_addr(struct sgx_epc_page *page)
>  	return section->virt_addr + index * PAGE_SIZE;
>  }
>  
> +struct sgx_epc_lru {
> +	spinlock_t lock;
> +	struct list_head reclaimable;

s/reclaimable/list/

> +};
> +
> +static inline void sgx_lru_init(struct sgx_epc_lru *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);
>  
> -- 
> 2.37.3
> 

Please also add these:

/*
 * Must be called with queue->lock acquired.
 */
static inline struct sgx_epc_page *__sgx_epc_queue_push(struct sgx_epc_queue *queue,
                                                        struct sgx_page *page)
{
        list_add_tail(&page->list, &queue->list);
}

/*
 * Must be called with queue->lock acquired.
 */
static inline struct sgx_epc_page *__sgx_epc_queue_pop(struct sgx_epc_queue *queue)
{
        struct sgx_epc_page *page;

        if (list_empty(&queue->list)
                return NULL;

	page = list_first_entry(&queue->list, struct sgx_epc_page, list);
  	list_del_init(&page->list);

        return page;
}

And use them in existing sites. It ensures coherent behavior. You should be
able to replace all uses with either, or combination of them (list_move).

BR, Jarkko