[PATCH v15 17/23] 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.

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/include/asm/sgx.h      |  4 ++
 arch/x86/kernel/cpu/intel_sgx.c | 77 +++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
index aa51165eb3a8..4e39bcfad018 100644
--- a/arch/x86/include/asm/sgx.h
+++ b/arch/x86/include/asm/sgx.h
@@ -309,4 +309,8 @@ static inline int __emodt(struct sgx_secinfo *secinfo, void 
__iomem *addr)
        return __encls_ret_2(SGX_EMODT, secinfo, addr);
 }
 
+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 /* _ASM_X86_SGX_H */
diff --git a/arch/x86/kernel/cpu/intel_sgx.c b/arch/x86/kernel/cpu/intel_sgx.c
index b86aa4111592..b06709a9ea65 100644
--- a/arch/x86/kernel/cpu/intel_sgx.c
+++ b/arch/x86/kernel/cpu/intel_sgx.c
@@ -15,6 +15,83 @@ EXPORT_SYMBOL_GPL(sgx_epc_sections);
 
 static int sgx_nr_epc_sections;
 
+/**
+ * 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);
+               if (section->free_cnt) {
+                       page = section->pages[section->free_cnt - 1];
+                       section->free_cnt--;
+               }
+               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);
+       section->pages[section->free_cnt++] = page;
+       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)
 {
        int i;
-- 
2.19.1