linux-kernel - [PATCH v15 17/23] x86/sgx: Add functions to allocate and free EPC pages

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Date:   Sat,  3 Nov 2018 01:11:16 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        linux-sgx@...r.kernel.org
Cc:     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,
        mark.shanahan@...el.com, andriy.shevchenko@...ux.intel.com,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT))
Subject: [PATCH v15 17/23] 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.

Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.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