Re: [PATCH v5 06/18] x86/sgx: Introduce EPC page states

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

On Sat Sep 23, 2023 at 6:06 AM EEST, Haitao Huang wrote:
> Use the lower 3 bits in the flags field of sgx_epc_page struct to
> track EPC states in its life cycle and define an enum for possible
> states. More state(s) will be added later.
>
> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
> ---
> V4:
> - No changes other than required for patch reordering.
>
> V3:
> - This is new in V3 to replace the bit mask based approach (requested by Jarkko)
> ---
>  arch/x86/kernel/cpu/sgx/encl.c  | 14 +++++++---
>  arch/x86/kernel/cpu/sgx/ioctl.c |  7 +++--
>  arch/x86/kernel/cpu/sgx/main.c  | 19 +++++++------
>  arch/x86/kernel/cpu/sgx/sgx.h   | 49 ++++++++++++++++++++++++++++++---
>  4 files changed, 71 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 97a53e34a8b4..f5afc8d65e22 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -244,8 +244,12 @@ static struct sgx_epc_page *sgx_encl_load_secs(struct sgx_encl *encl)
>  {
>  	struct sgx_epc_page *epc_page = encl->secs.epc_page;
>  
> -	if (!epc_page)
> +	if (!epc_page) {
>  		epc_page = sgx_encl_eldu(&encl->secs, NULL);
> +		if (!IS_ERR(epc_page))
> +			sgx_record_epc_page(epc_page,
> +					    SGX_EPC_PAGE_UNRECLAIMABLE);

Can be a single line probably (less than 100 characters).

> +	}
>  
>  	return epc_page;
>  }
> @@ -272,7 +276,7 @@ static struct sgx_encl_page *__sgx_encl_load_page(struct sgx_encl *encl,
>  		return ERR_CAST(epc_page);
>  
>  	encl->secs_child_cnt++;
> -	sgx_record_epc_page(epc_page, SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +	sgx_record_epc_page(epc_page, SGX_EPC_PAGE_RECLAIMABLE);
>  
>  	return entry;
>  }
> @@ -398,7 +402,7 @@ static vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
>  	encl_page->type = SGX_PAGE_TYPE_REG;
>  	encl->secs_child_cnt++;
>  
> -	sgx_record_epc_page(epc_page, SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +	sgx_record_epc_page(epc_page, SGX_EPC_PAGE_RECLAIMABLE);
>  
>  	phys_addr = sgx_get_epc_phys_addr(epc_page);
>  	/*
> @@ -1256,6 +1260,8 @@ struct sgx_epc_page *sgx_alloc_va_page(bool reclaim)
>  		sgx_encl_free_epc_page(epc_page);
>  		return ERR_PTR(-EFAULT);
>  	}
> +	sgx_record_epc_page(epc_page,
> +			    SGX_EPC_PAGE_UNRECLAIMABLE);

There is bunch of these apparently.

>  
>  	return epc_page;
>  }
> @@ -1315,7 +1321,7 @@ void sgx_encl_free_epc_page(struct sgx_epc_page *page)
>  {
>  	int ret;
>  
> -	WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +	WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_STATE_MASK);
>  
>  	ret = __eremove(sgx_get_epc_virt_addr(page));
>  	if (WARN_ONCE(ret, EREMOVE_ERROR_MESSAGE, ret, ret))
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index a75eb44022a3..9a32bf5a1070 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -113,6 +113,9 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
>  	encl->attributes = secs->attributes;
>  	encl->attributes_mask = SGX_ATTR_UNPRIV_MASK;
>  
> +	sgx_record_epc_page(encl->secs.epc_page,
> +			    SGX_EPC_PAGE_UNRECLAIMABLE);
> +
>  	/* Set only after completion, as encl->lock has not been taken. */
>  	set_bit(SGX_ENCL_CREATED, &encl->flags);
>  
> @@ -322,7 +325,7 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long src,
>  			goto err_out;
>  	}
>  
> -	sgx_record_epc_page(epc_page, SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +	sgx_record_epc_page(epc_page, SGX_EPC_PAGE_RECLAIMABLE);
>  	mutex_unlock(&encl->lock);
>  	mmap_read_unlock(current->mm);
>  	return ret;
> @@ -976,7 +979,7 @@ static long sgx_enclave_modify_types(struct sgx_encl *encl,
>  
>  			mutex_lock(&encl->lock);
>  
> -			sgx_record_epc_page(entry->epc_page, SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +			sgx_record_epc_page(entry->epc_page, SGX_EPC_PAGE_RECLAIMABLE);
>  		}
>  
>  		/* Change EPC type */
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index dec1d57cbff6..b26860399402 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -318,7 +318,7 @@ static void sgx_reclaim_pages(void)
>  			/* The owner is freeing the page. No need to add the
>  			 * page back to the list of reclaimable pages.
>  			 */
> -			epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
> +			sgx_epc_page_reset_state(epc_page);
>  	}
>  	spin_unlock(&sgx_global_lru.lock);
>  
> @@ -344,6 +344,7 @@ static void sgx_reclaim_pages(void)
>  
>  skip:
>  		spin_lock(&sgx_global_lru.lock);
> +		sgx_epc_page_set_state(epc_page, SGX_EPC_PAGE_RECLAIMABLE);
>  		list_add_tail(&epc_page->list, &sgx_global_lru.reclaimable);
>  		spin_unlock(&sgx_global_lru.lock);
>  
> @@ -367,7 +368,7 @@ static void sgx_reclaim_pages(void)
>  		sgx_reclaimer_write(epc_page, &backing[i]);
>  
>  		kref_put(&encl_page->encl->refcount, sgx_encl_release);
> -		epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
> +		sgx_epc_page_reset_state(epc_page);
>  
>  		sgx_free_epc_page(epc_page);
>  	}
> @@ -507,9 +508,9 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
>  void sgx_record_epc_page(struct sgx_epc_page *page, unsigned long flags)
>  {
>  	spin_lock(&sgx_global_lru.lock);
> -	WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +	WARN_ON_ONCE(sgx_epc_page_reclaimable(page->flags));
>  	page->flags |= flags;
> -	if (flags & SGX_EPC_PAGE_RECLAIMER_TRACKED)
> +	if (sgx_epc_page_reclaimable(flags))
>  		list_add_tail(&page->list, &sgx_global_lru.reclaimable);
>  	spin_unlock(&sgx_global_lru.lock);
>  }
> @@ -527,7 +528,7 @@ void sgx_record_epc_page(struct sgx_epc_page *page, unsigned long flags)
>  int sgx_drop_epc_page(struct sgx_epc_page *page)
>  {
>  	spin_lock(&sgx_global_lru.lock);
> -	if (page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED) {
> +	if (sgx_epc_page_reclaimable(page->flags)) {
>  		/* The page is being reclaimed. */
>  		if (list_empty(&page->list)) {
>  			spin_unlock(&sgx_global_lru.lock);
> @@ -535,7 +536,7 @@ int sgx_drop_epc_page(struct sgx_epc_page *page)
>  		}
>  
>  		list_del(&page->list);
> -		page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
> +		sgx_epc_page_reset_state(page);
>  	}
>  	spin_unlock(&sgx_global_lru.lock);
>  
> @@ -607,6 +608,8 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>  	struct sgx_epc_section *section = &sgx_epc_sections[page->section];
>  	struct sgx_numa_node *node = section->node;
>  
> +	WARN_ON_ONCE(page->flags & (SGX_EPC_PAGE_STATE_MASK));
> +
>  	spin_lock(&node->lock);
>  
>  	page->owner = NULL;
> @@ -614,7 +617,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>  		list_add(&page->list, &node->sgx_poison_page_list);
>  	else
>  		list_add_tail(&page->list, &node->free_page_list);
> -	page->flags = SGX_EPC_PAGE_IS_FREE;
> +	page->flags = SGX_EPC_PAGE_FREE;
>  
>  	spin_unlock(&node->lock);
>  	atomic_long_inc(&sgx_nr_free_pages);
> @@ -715,7 +718,7 @@ int arch_memory_failure(unsigned long pfn, int flags)
>  	 * If the page is on a free list, move it to the per-node
>  	 * poison page list.
>  	 */
> -	if (page->flags & SGX_EPC_PAGE_IS_FREE) {
> +	if (page->flags == SGX_EPC_PAGE_FREE) {
>  		list_move(&page->list, &node->sgx_poison_page_list);
>  		goto out;
>  	}
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 113d930fd087..2faeb40b345f 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -23,11 +23,36 @@
>  #define SGX_NR_LOW_PAGES		32
>  #define SGX_NR_HIGH_PAGES		64
>  
> -/* Pages, which are being tracked by the page reclaimer. */
> -#define SGX_EPC_PAGE_RECLAIMER_TRACKED	BIT(0)
> +enum sgx_epc_page_state {
> +	/* Not tracked by the reclaimer:
> +	 * Pages allocated for virtual EPC which are never tracked by the host
> +	 * reclaimer; pages just allocated from free list but not yet put in
> +	 * use; pages just reclaimed, but not yet returned to the free list.
> +	 * Becomes FREE after sgx_free_epc()
> +	 * Becomes RECLAIMABLE or UNRECLAIMABLE after sgx_record_epc()
> +	 */
> +	SGX_EPC_PAGE_NOT_TRACKED = 0,
> +
> +	/* Page is in the free list, ready for allocation
> +	 * Becomes NOT_TRACKED after sgx_alloc_epc_page()
> +	 */
> +	SGX_EPC_PAGE_FREE = 1,
> +
> +	/* Page is in use and tracked in a reclaimable LRU list
> +	 * Becomes NOT_TRACKED after sgx_drop_epc()
> +	 */
> +	SGX_EPC_PAGE_RECLAIMABLE = 2,
> +
> +	/* Page is in use but tracked in an unreclaimable LRU list. These are
> +	 * only reclaimable when the whole enclave is OOM killed or the enclave
> +	 * is released, e.g., VA, SECS pages
> +	 * Becomes NOT_TRACKED after sgx_drop_epc()
> +	 */
> +	SGX_EPC_PAGE_UNRECLAIMABLE = 3,
>  
> -/* Pages on free list */
> -#define SGX_EPC_PAGE_IS_FREE		BIT(1)
> +};
> +
> +#define SGX_EPC_PAGE_STATE_MASK GENMASK(2, 0)
>  
>  struct sgx_epc_page {
>  	unsigned int section;
> @@ -37,6 +62,22 @@ struct sgx_epc_page {
>  	struct list_head list;
>  };
>  
> +static inline void sgx_epc_page_reset_state(struct sgx_epc_page *page)
> +{
> +	page->flags &= ~SGX_EPC_PAGE_STATE_MASK;
> +}
> +
> +static inline void sgx_epc_page_set_state(struct sgx_epc_page *page, unsigned long flags)
> +{
> +	page->flags &= ~SGX_EPC_PAGE_STATE_MASK;
> +	page->flags |= (flags & SGX_EPC_PAGE_STATE_MASK);
> +}
> +
> +static inline bool sgx_epc_page_reclaimable(unsigned long flags)
> +{
> +	return SGX_EPC_PAGE_RECLAIMABLE == (flags & SGX_EPC_PAGE_STATE_MASK);
> +}
> +
>  /*
>   * Contains the tracking data for NUMA nodes having EPC pages. Most importantly,
>   * the free page list local to the node is stored here.
> -- 
> 2.25.1

BR, Jarkko