On Wed, 2021-09-22 at 11:21 -0700, Tony Luck wrote:
> SGX EPC pages go through the following life cycle:
>
> DIRTY ---> FREE ---> IN-USE --\
> ^ |
> \-----------------/
>
> Recovery action for poison for a DIRTY or FREE page is simple. Just
> make sure never to allocate the page. IN-USE pages need some extra
> handling.
>
> It would be good to use the sgx_epc_page->owner field as an indicator
> of where an EPC page is currently in that cycle (owner != NULL means
> the EPC page is IN-USE). But there is one caller, sgx_alloc_va_page(),
> that calls with NULL.
>
> Since there are multiple uses of the "owner" field with different types
> change the type of sgx_epc_page.owner to "void *.
>
> Start epc_pages out with a non-NULL owner while they are in DIRTY state.
>
> Fix up the one holdout to provide a non-NULL owner.
>
> Refactor the allocation sequence so that changes to/from NULL
> value happen together with adding/removing the epc_page from
> a free list while the node->lock is held.
>
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> arch/x86/kernel/cpu/sgx/encl.c | 5 +++--
> arch/x86/kernel/cpu/sgx/encl.h | 2 +-
> arch/x86/kernel/cpu/sgx/ioctl.c | 2 +-
> arch/x86/kernel/cpu/sgx/main.c | 21 +++++++++++----------
> arch/x86/kernel/cpu/sgx/sgx.h | 4 ++--
> 5 files changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 001808e3901c..62cf20d5fbf6 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -667,6 +667,7 @@ int sgx_encl_test_and_clear_young(struct mm_struct *mm,
>
> /**
> * sgx_alloc_va_page() - Allocate a Version Array (VA) page
> + * @owner: struct sgx_va_page connected to this VA page
> *
> * Allocate a free EPC page and convert it to a Version Array (VA) page.
> *
> @@ -674,12 +675,12 @@ int sgx_encl_test_and_clear_young(struct mm_struct *mm,
> * a VA page,
> * -errno otherwise
> */
> -struct sgx_epc_page *sgx_alloc_va_page(void)
> +struct sgx_epc_page *sgx_alloc_va_page(void *owner)
> {
> struct sgx_epc_page *epc_page;
> int ret;
>
> - epc_page = sgx_alloc_epc_page(NULL, true);
> + epc_page = sgx_alloc_epc_page(owner, true);
> if (IS_ERR(epc_page))
> return ERR_CAST(epc_page);
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
> index fec43ca65065..2a972bc9b2d1 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -111,7 +111,7 @@ void sgx_encl_put_backing(struct sgx_backing *backing, bool do_write);
> int sgx_encl_test_and_clear_young(struct mm_struct *mm,
> struct sgx_encl_page *page);
>
> -struct sgx_epc_page *sgx_alloc_va_page(void);
> +struct sgx_epc_page *sgx_alloc_va_page(void *owner);
> unsigned int sgx_alloc_va_slot(struct sgx_va_page *va_page);
> void sgx_free_va_slot(struct sgx_va_page *va_page, unsigned int offset);
> bool sgx_va_page_full(struct sgx_va_page *va_page);
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 83df20e3e633..655ce0bb069d 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -30,7 +30,7 @@ static struct sgx_va_page *sgx_encl_grow(struct sgx_encl *encl)
> if (!va_page)
> return ERR_PTR(-ENOMEM);
>
> - va_page->epc_page = sgx_alloc_va_page();
> + va_page->epc_page = sgx_alloc_va_page(va_page);
> if (IS_ERR(va_page->epc_page)) {
> err = ERR_CAST(va_page->epc_page);
> kfree(va_page);
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 63d3de02bbcc..69743709ec90 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -457,7 +457,7 @@ static bool __init sgx_page_reclaimer_init(void)
> return true;
> }
>
> -static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
> +static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(void *owner, int nid)
> {
> struct sgx_numa_node *node = &sgx_numa_nodes[nid];
> struct sgx_epc_page *page = NULL;
> @@ -471,6 +471,7 @@ static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
>
> page = list_first_entry(&node->free_page_list, struct sgx_epc_page, list);
> list_del_init(&page->list);
> + page->owner = owner;
> sgx_nr_free_pages--;
>
> spin_unlock(&node->lock);
> @@ -480,6 +481,7 @@ static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
>
> /**
> * __sgx_alloc_epc_page() - Allocate an EPC page
> + * @owner: the owner of the EPC page
> *
> * Iterate through NUMA nodes and reserve ia free EPC page to the caller. Start
> * from the NUMA node, where the caller is executing.
> @@ -488,14 +490,14 @@ static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
> * - an EPC page: A borrowed EPC pages were available.
> * - NULL: Out of EPC pages.
> */
> -struct sgx_epc_page *__sgx_alloc_epc_page(void)
> +struct sgx_epc_page *__sgx_alloc_epc_page(void *owner)
> {
> struct sgx_epc_page *page;
> int nid_of_current = numa_node_id();
> int nid = nid_of_current;
>
> if (node_isset(nid_of_current, sgx_numa_mask)) {
> - page = __sgx_alloc_epc_page_from_node(nid_of_current);
> + page = __sgx_alloc_epc_page_from_node(owner, nid_of_current);
> if (page)
> return page;
> }
> @@ -506,7 +508,7 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
> if (nid == nid_of_current)
> break;
>
> - page = __sgx_alloc_epc_page_from_node(nid);
> + page = __sgx_alloc_epc_page_from_node(owner, nid);
> if (page)
> return page;
> }
> @@ -559,7 +561,7 @@ int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
>
> /**
> * sgx_alloc_epc_page() - Allocate an EPC page
> - * @owner: the owner of the EPC page
> + * @owner: per-caller page owner
> * @reclaim: reclaim pages if necessary
> *
> * Iterate through EPC sections and borrow a free EPC page to the caller. When a
> @@ -579,11 +581,9 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> struct sgx_epc_page *page;
>
> for ( ; ; ) {
> - page = __sgx_alloc_epc_page();
> - if (!IS_ERR(page)) {
> - page->owner = owner;
> + page = __sgx_alloc_epc_page(owner);
> + if (!IS_ERR(page))
> break;
> - }
>
> if (list_empty(&sgx_active_page_list))
> return ERR_PTR(-ENOMEM);
> @@ -624,6 +624,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>
> spin_lock(&node->lock);
>
> + page->owner = NULL;
> list_add_tail(&page->list, &node->free_page_list);
> sgx_nr_free_pages++;
>
> @@ -652,7 +653,7 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
> for (i = 0; i < nr_pages; i++) {
> section->pages[i].section = index;
> section->pages[i].flags = 0;
> - section->pages[i].owner = NULL;
> + section->pages[i].owner = (void *)-1;
Probably should have a named constant.
Anyway, I wonder why we want to do tricks with 'owner', when the
struct has a flags field?
Right now its use is so nice and straight forward, and most
importantly intuitive.
So what I would do instead of this, would be to add something
like
/* Pages, which are being tracked by the page reclaimer. */
#define SGX_EPC_PAGE_RECLAIMER_TRACKED BIT(0)
/* Pages, which are allocated for use. */
#define SGX_EPC_PAGE_ALLOCATED BIT(1)
This would be set by sgx_alloc_epc_page() and reset by
sgx_free_epc_page().
In the subsequent patch you could then instead of
/*
* If there is no owner, then the page is on a free list.
* Move it to the poison page list.
*/
if (!page->owner) {
list_del(&page->list);
list_add(&page->list, &sgx_poison_page_list);
goto out;
}
you would
/*
* If there is no owner, then the page is on a free list.
* Move it to the poison page list.
*/
if (!page->flags) {
list_del(&page->list);
list_add(&page->list, &sgx_poison_page_list);
goto out;
}
You don't actually need to compare to that flag because the
invariant would be that it is set, as long as the page is
not explicitly freed.
I think this is a better solution than in the patch set
because it does not introduce any unorthodox use of anything.
/Jarkko
