[PATCH v21 13/28] x86/sgx: Add functions to allocate and free EPC pages

[Jarkko Sakkinen]

At this time there is no support for reclaiming pages prior to the
owner explicitly freeing the page.  As for freeing pages, because
freeing a page is expected to succeed in the vast majority of cases
and because most call sites will not be equipped to handle failure,
provide a variant for freeing a page that warns on failure, e.g. due
to ENCLS[EREMOVE] failing.

Signed-off-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopher...@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com>
---
 arch/x86/kernel/cpu/sgx/main.c | 90 ++++++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/sgx/sgx.h  |  4 ++
 2 files changed, 94 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index e2317f6e4374..6b4727df72ca 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -9,6 +9,7 @@
 #include <linux/sched/signal.h>
 #include <linux/slab.h>
 #include "arch.h"
+#include "encls.h"
 #include "sgx.h"
 
 struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
@@ -16,6 +17,95 @@ EXPORT_SYMBOL_GPL(sgx_epc_sections);
 
 int sgx_nr_epc_sections;
 
+static struct sgx_epc_page *sgx_section_get_page(
+       struct sgx_epc_section *section)
+{
+       struct sgx_epc_page *page;
+
+       if (!section->free_cnt)
+               return NULL;
+
+       page = list_first_entry(&section->page_list,
+                               struct sgx_epc_page, list);
+       list_del_init(&page->list);
+       section->free_cnt--;
+       return page;
+}
+
+/**
+ * sgx_alloc_page - Allocate an EPC page
+ *
+ * Try to grab a page from the free EPC page list.
+ *
+ * Return:
+ *   a pointer to a &struct sgx_epc_page instance,
+ *   -errno on error
+ */
+struct sgx_epc_page *sgx_alloc_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_section_get_page(section);
+               spin_unlock(&section->lock);
+
+               if (page)
+                       return page;
+       }
+
+       return ERR_PTR(-ENOMEM);
+}
+EXPORT_SYMBOL_GPL(sgx_alloc_page);
+
+/**
+ * __sgx_free_page - Free an EPC page
+ * @page:      pointer a previously allocated EPC page
+ *
+ * EREMOVE an EPC page and insert it back to the list of free pages.
+ *
+ * Return:
+ *   0 on success
+ *   SGX error code if EREMOVE fails
+ */
+int __sgx_free_page(struct sgx_epc_page *page)
+{
+       struct sgx_epc_section *section = sgx_epc_section(page);
+       int ret;
+
+       ret = __eremove(sgx_epc_addr(page));
+       if (ret)
+               return ret;
+
+       spin_lock(&section->lock);
+       list_add_tail(&page->list, &section->page_list);
+       section->free_cnt++;
+       spin_unlock(&section->lock);
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(__sgx_free_page);
+
+/**
+ * sgx_free_page - Free an EPC page and WARN on failure
+ * @page:      pointer to a previously allocated EPC page
+ *
+ * EREMOVE an EPC page and insert it back to the list of free pages, and WARN
+ * if EREMOVE fails.  For use when the call site cannot (or chooses not to)
+ * handle failure, i.e. the page is leaked on failure.
+ */
+void sgx_free_page(struct sgx_epc_page *page)
+{
+       int ret;
+
+       ret = __sgx_free_page(page);
+       WARN(ret > 0, "sgx: EREMOVE returned %d (0x%x)", ret, ret);
+}
+EXPORT_SYMBOL_GPL(sgx_free_page);
+
 static __init void 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 3009ec816339..210510a28ce0 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -64,4 +64,8 @@ extern int sgx_nr_epc_sections;
 
 int sgx_page_reclaimer_init(void);
 
+struct sgx_epc_page *sgx_alloc_page(void);
+int __sgx_free_page(struct sgx_epc_page *page);
+void sgx_free_page(struct sgx_epc_page *page);
+
 #endif /* _X86_SGX_H */
-- 
2.20.1