Re: [PATCH v4 09/18] x86/sgx: Store struct sgx_encl when allocating new VA pages

From: Jarkko Sakkinen
Date: Wed Sep 13 2023 - 11:31:52 EST

On Wed Sep 13, 2023 at 7:06 AM EEST, Haitao Huang wrote:
> In a later patch, when a cgroup has exceeded the max capacity for EPC
> pages, it may need to identify and OOM kill a less active enclave to
> make room for other enclaves within the same group. Such a victim
> enclave would have no active pages other than the unreclaimable Version
> Array (VA) and SECS pages. Therefore, the cgroup needs examine its
> unreclaimable page list, and finding an enclave given a SECS page or a
> VA page. This will require a backpointer from a page to an enclave,
> which is not available for VA pages.
>
> Because struct sgx_epc_page instances of VA pages are not owned by an
> sgx_encl_page instance, mark their owner as sgx_encl: pass the struct
> sgx_encl of the enclave allocating the VA page to sgx_alloc_epc_page(),
> which will store this value in the owner field of the struct
> sgx_epc_page. In a later patch, VA pages will be placed in an
> unreclaimable queue that can be examined by the cgroup to select the OOM
> killed enclave.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
> Signed-off-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> V4:
> - Changes needed for patch reordering
> - Revised commit messages (Jarkko)
> ---
> 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 | 20 ++++++++++----------
> arch/x86/kernel/cpu/sgx/sgx.h | 5 ++++-
> 5 files changed, 19 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index d11d4111aa98..1aee0ad00e66 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -1238,6 +1238,7 @@ void sgx_zap_enclave_ptes(struct sgx_encl *encl, unsigned long addr)
>
> /**
> * sgx_alloc_va_page() - Allocate a Version Array (VA) page
> + * @encl: The enclave that this page is allocated to.

Maybe would more clear:

* @encl: The new owner of the page

> * @reclaim: Reclaim EPC pages directly if none available. Enclave
> * mutex should not be held if this is set.
> *
> @@ -1247,12 +1248,12 @@ void sgx_zap_enclave_ptes(struct sgx_encl *encl, unsigned long addr)
> * a VA page,
> * -errno otherwise
> */
> -struct sgx_epc_page *sgx_alloc_va_page(bool reclaim)
> +struct sgx_epc_page *sgx_alloc_va_page(struct sgx_encl *encl, bool reclaim)
> {
> struct sgx_epc_page *epc_page;
> int ret;
>
> - epc_page = sgx_alloc_epc_page(NULL, reclaim);
> + epc_page = sgx_alloc_epc_page(encl, reclaim);
> 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 f94ff14c9486..831d63f80f5a 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -116,7 +116,7 @@ struct sgx_encl_page *sgx_encl_page_alloc(struct sgx_encl *encl,
> unsigned long offset,
> u64 secinfo_flags);
> void sgx_zap_enclave_ptes(struct sgx_encl *encl, unsigned long addr);
> -struct sgx_epc_page *sgx_alloc_va_page(bool reclaim);
> +struct sgx_epc_page *sgx_alloc_va_page(struct sgx_encl *encl, bool reclaim);
> 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 c28f074d5d71..3ab8c050e665 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -30,7 +30,7 @@ struct sgx_va_page *sgx_encl_grow(struct sgx_encl *encl, bool reclaim)
> if (!va_page)
> return ERR_PTR(-ENOMEM);
>
> - va_page->epc_page = sgx_alloc_va_page(reclaim);
> + va_page->epc_page = sgx_alloc_va_page(encl, reclaim);
> 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 fba06dc5abfe..ed813288af44 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -107,7 +107,7 @@ static unsigned long __sgx_sanitize_pages(struct list_head *dirty_page_list)
>
> static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
> {
> - struct sgx_encl_page *page = epc_page->owner;
> + struct sgx_encl_page *page = epc_page->encl_page;
> struct sgx_encl *encl = page->encl;
> struct sgx_encl_mm *encl_mm;
> bool ret = true;
> @@ -139,7 +139,7 @@ static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
>
> static void sgx_reclaimer_block(struct sgx_epc_page *epc_page)
> {
> - struct sgx_encl_page *page = epc_page->owner;
> + struct sgx_encl_page *page = epc_page->encl_page;
> unsigned long addr = page->desc & PAGE_MASK;
> struct sgx_encl *encl = page->encl;
> int ret;
> @@ -196,7 +196,7 @@ void sgx_ipi_cb(void *info)
> static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
> struct sgx_backing *backing)
> {
> - struct sgx_encl_page *encl_page = epc_page->owner;
> + struct sgx_encl_page *encl_page = epc_page->encl_page;
> struct sgx_encl *encl = encl_page->encl;
> struct sgx_va_page *va_page;
> unsigned int va_offset;
> @@ -249,7 +249,7 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
> static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
> struct sgx_backing *backing)
> {
> - struct sgx_encl_page *encl_page = epc_page->owner;
> + struct sgx_encl_page *encl_page = epc_page->encl_page;
> struct sgx_encl *encl = encl_page->encl;
> struct sgx_backing secs_backing;
> int ret;
> @@ -309,7 +309,7 @@ static void sgx_reclaim_pages(void)
> break;
>
> list_del_init(&epc_page->list);
> - encl_page = epc_page->owner;
> + encl_page = epc_page->encl_page;
>
> if (kref_get_unless_zero(&encl_page->encl->refcount) != 0) {
> sgx_epc_page_set_state(epc_page, SGX_EPC_PAGE_RECLAIM_IN_PROGRESS);
> @@ -329,7 +329,7 @@ static void sgx_reclaim_pages(void)
>
> i = 0;
> list_for_each_entry_safe(epc_page, tmp, &iso, list) {
> - encl_page = epc_page->owner;
> + encl_page = epc_page->encl_page;
>
> if (!sgx_reclaimer_age(epc_page))
> goto skip;
> @@ -362,7 +362,7 @@ static void sgx_reclaim_pages(void)
>
> i = 0;
> list_for_each_entry_safe(epc_page, tmp, &iso, list) {
> - encl_page = epc_page->owner;
> + encl_page = epc_page->encl_page;
> sgx_reclaimer_write(epc_page, &backing[i++]);
>
> kref_put(&encl_page->encl->refcount, sgx_encl_release);
> @@ -562,7 +562,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> for ( ; ; ) {
> page = __sgx_alloc_epc_page();
> if (!IS_ERR(page)) {
> - page->owner = owner;
> + page->encl_page = owner;
> break;
> }
>
> @@ -607,7 +607,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>
> spin_lock(&node->lock);
>
> - page->owner = NULL;
> + page->encl_page = NULL;
> if (page->poison)
> list_add(&page->list, &node->sgx_poison_page_list);
> else
> @@ -642,7 +642,7 @@ 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].encl_page = NULL;
> section->pages[i].poison = 0;
> list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
> }
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 764cec23f4e5..c75ddc7168fa 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -68,7 +68,10 @@ struct sgx_epc_page {
> unsigned int section;
> u16 flags;
> u16 poison;
> - struct sgx_encl_page *owner;

/* possible owner types */
> + union {
> + struct sgx_encl_page *encl_page;
> + struct sgx_encl *encl;
> + };
> struct list_head list;
> };
>
> --
> 2.25.1

BR, Jarkko