linux-kernel - [PATCH v20 13/28] x86/sgx: Add functions to allocate and free EPC pages

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Date:   Wed, 17 Apr 2019 13:39:23 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org
Cc:     akpm@...ux-foundation.org, dave.hansen@...el.com,
        sean.j.christopherson@...el.com, nhorman@...hat.com,
        npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        kai.svahn@...el.com, bp@...en8.de, josh@...htriplett.org,
        luto@...nel.org, kai.huang@...el.com, rientjes@...gle.com,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Subject: [PATCH v20 13/28] x86/sgx: Add functions to allocate and free EPC pages

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.sakkinen@...ux.intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.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 */
-- 
2.19.1