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

Jarkko Sakkinen
2022-09-23T13:20:28Z

On Thu, Sep 22, 2022 at 10:10:41AM -0700, Kristen Carlson Accardi wrote:
> From: Sean Christopherson <sean.j.christopherson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>
> 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-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Kristen Carlson Accardi <kristen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
> Cc: Sean Christopherson <seanjc-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

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