x86/sgx: Add SGX page allocator functions

Add functions for runtime allocation and free.

This allocator and its algorithms are as simple as it gets.  They do a
linear search across all EPC sections and find the first free page.  They
are not NUMA-aware and only hand out individual pages.  The SGX hardware
does not support large pages, so something more complicated like a buddy
allocator is unwarranted.

The free function (sgx_free_epc_page()) implicitly calls ENCLS[EREMOVE],
which returns the page to the uninitialized state.  This ensures that the
page is ready for use at the next allocation.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Jethro Beekman <jethro@fortanix.com>
Link: https://lkml.kernel.org/r/20201112220135.165028-10-jarkko@kernel.org

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 187a237..2e53afc 100644 (file)
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -85,6 +85,71 @@ 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;
+
+       spin_lock(&section->lock);
+
+       if (list_empty(&section->page_list)) {
+               spin_unlock(&section->lock);
+               return NULL;
+       }
+
+       page = list_first_entry(&section->page_list, struct sgx_epc_page, list);
+       list_del_init(&page->list);
+
+       spin_unlock(&section->lock);
+       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];
+
+               page = __sgx_alloc_epc_page_from_section(section);
+               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_epc_sections[page->section];
+       int ret;
+
+       ret = __eremove(sgx_get_epc_virt_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 bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
                                         unsigned long index,
                                         struct sgx_epc_section *section)

diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 02afa84..bd9dcb1 100644 (file)
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -57,4 +57,7 @@ static inline void *sgx_get_epc_virt_addr(struct sgx_epc_page *page)
        return section->virt_addr + index * PAGE_SIZE;
 }
 
+struct sgx_epc_page *__sgx_alloc_epc_page(void);
+void sgx_free_epc_page(struct sgx_epc_page *page);
+
 #endif /* _X86_SGX_H */