[PATCH v39 09/24] x86/sgx: Add __sgx_alloc_epc_page() and sgx_free_epc_page()

[Jarkko Sakkinen]

Add __sgx_alloc_epc_page(), which iterates through EPC sections and borrows
a page structure that is not used by anyone else. When a page is no longer
needed it must be released with sgx_free_epc_page(). This function
implicitly calls ENCLS[EREMOVE], which will return the page to the
uninitialized state (i.e. not required from caller part).

Acked-by: Jethro Beekman <jet...@fortanix.com>
Reviewed-by: Darren Kenny <darren.ke...@oracle.com>
Co-developed-by: Sean Christopherson <sean.j.christopher...@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
---
 arch/x86/kernel/cpu/sgx/main.c | 62 ++++++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/sgx/sgx.h  |  3 ++
 2 files changed, 65 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index c5831e3db14a..97c6895fb6c9 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -83,6 +83,68 @@ static bool __init sgx_page_reclaimer_init(void)
        return true;
 }
 
+static struct sgx_epc_page *__sgx_alloc_epc_page_from_section(struct 
sgx_epc_section *section)
+{
+       struct sgx_epc_page *page;
+
+       if (list_empty(&section->page_list))
+               return NULL;
+
+       page = list_first_entry(&section->page_list, struct sgx_epc_page, list);
+       list_del_init(&page->list);
+
+       return page;
+}
+
+/**
+ * __sgx_alloc_epc_page() - Allocate an EPC page
+ *
+ * Iterate through EPC sections and borrow a free EPC page to the caller. When 
a
+ * page is no longer needed it must be released with sgx_free_epc_page().
+ *
+ * Return:
+ *   an EPC page,
+ *   -errno on error
+ */
+struct sgx_epc_page *__sgx_alloc_epc_page(void)
+{
+       struct sgx_epc_section *section;
+       struct sgx_epc_page *page;
+       int i;
+
+       for (i = 0; i < sgx_nr_epc_sections; i++) {
+               section = &sgx_epc_sections[i];
+               spin_lock(&section->lock);
+               page = __sgx_alloc_epc_page_from_section(section);
+               spin_unlock(&section->lock);
+
+               if (page)
+                       return page;
+       }
+
+       return ERR_PTR(-ENOMEM);
+}
+
+/**
+ * sgx_free_epc_page() - Free an EPC page
+ * @page:      an EPC page
+ *
+ * Call EREMOVE for an EPC page and insert it back to the list of free pages.
+ */
+void sgx_free_epc_page(struct sgx_epc_page *page)
+{
+       struct sgx_epc_section *section = sgx_get_epc_section(page);
+       int ret;
+
+       ret = __eremove(sgx_get_epc_addr(page));
+       if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
+               return;
+
+       spin_lock(&section->lock);
+       list_add_tail(&page->list, &section->page_list);
+       spin_unlock(&section->lock);
+}
+
 static void __init sgx_free_epc_section(struct sgx_epc_section *section)
 {
        struct sgx_epc_page *page;
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index dff4f5f16d09..fce756c3434b 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -49,4 +49,7 @@ static inline void *sgx_get_epc_addr(struct sgx_epc_page 
*page)
        return section->va + (page->desc & PAGE_MASK) - section->pa;
 }
 
+struct sgx_epc_page *__sgx_alloc_epc_page(void);
+void sgx_free_epc_page(struct sgx_epc_page *page);
+
 #endif /* _X86_SGX_H */
-- 
2.25.1