linux-kernel - [PATCH v3 1/7] x86/sgx: Provide indication of life-cycle of EPC pages

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Date:   Wed, 28 Jul 2021 13:46:47 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCH v3 1/7] x86/sgx: Provide indication of life-cycle of EPC pages

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.

Make the following changes:

1) Change the type of "owner" to "void *" (it can have other types
   besides "struct sgx_encl_page *).
2) Add a check to sgx_free_epc_page(). If the caller specified the
   owner as NULL, then set the owner field to self-reference the
   SGX epc page itself.
3) Reset owner to NULL in sgx_free_epc_page().

Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/kernel/cpu/sgx/main.c | 3 ++-
 arch/x86/kernel/cpu/sgx/sgx.h  | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 63d3de02bbcc..17d09186a6c2 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -581,7 +581,7 @@ 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->owner = owner ? owner : page;
 			break;
 		}

@@ -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++;

diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 4628acec0009..4e1a410b8a62 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -29,7 +29,7 @@
 struct sgx_epc_page {
 	unsigned int section;
 	unsigned int flags;
-	struct sgx_encl_page *owner;
+	void *owner;
 	struct list_head list;
 };

-- 
2.29.2