[PATCH v4] x86/sgx: Do not consider unsanitized pages an error

[Jarkko Sakkinen <jarkko@kernel.org>]

In sgx_init(), if misc_register() for the provision device fails, and
neither sgx_drv_init() nor sgx_vepc_init() succeeds, then ksgxd will be
prematurely stopped.

This triggers WARN_ON() because sgx_dirty_page_list ends up being
non-empty. Ultimately this can crash the kernel, depending on the kernel
command line, which is not correct behavior because SGX driver is not
working incorrectly.

Print simple warning instead, and improve the output by printing the
number of unsanitized pages.

Link: https://lore.kernel.org/linux-sgx/20220825051827.246698-1-jarkko@kernel.org/T/#u
Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Fixes: 51ab30eb2ad4 ("x86/sgx: Replace section->init_laundry_list with sgx_dirty_page_list")
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
Cc: Haitao Huang <haitao.huang@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>

v4:
- Explain expectations for dirty_page_list in the function header, instead
  of an inline comment.
- Improve commit message to explain the conditions better.
- Return the number of pages left dirty to ksgxd() and print warning after
  the 2nd call, if there are any.

v3:
- Remove WARN_ON().
- Tuned comments and the commit message a bit.

v2:
- Replaced WARN_ON() with optional pr_info() inside
  __sgx_sanitize_pages().
- Rewrote the commit message.
- Added the fixes tag.
---
 arch/x86/kernel/cpu/sgx/main.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 515e2a5f25bb..903100fcfce3 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -49,17 +49,20 @@ static LIST_HEAD(sgx_dirty_page_list);
  * Reset post-kexec EPC pages to the uninitialized state. The pages are removed
  * from the input list, and made available for the page allocator. SECS pages
  * prepending their children in the input list are left intact.
+ *
+ * Contents of the @dirty_page_list must be thread-local, i.e.
+ * not shared by multiple threads.
  */
-static void __sgx_sanitize_pages(struct list_head *dirty_page_list)
+static int __sgx_sanitize_pages(struct list_head *dirty_page_list)
 {
 	struct sgx_epc_page *page;
+	int left_dirty = 0;
 	LIST_HEAD(dirty);
 	int ret;
 
-	/* dirty_page_list is thread-local, no need for a lock: */
 	while (!list_empty(dirty_page_list)) {
 		if (kthread_should_stop())
-			return;
+			break;
 
 		page = list_first_entry(dirty_page_list, struct sgx_epc_page, list);
 
@@ -92,12 +95,14 @@ static void __sgx_sanitize_pages(struct list_head *dirty_page_list)
 		} else {
 			/* The page is not yet clean - move to the dirty list. */
 			list_move_tail(&page->list, &dirty);
+			left_dirty++;
 		}
 
 		cond_resched();
 	}
 
 	list_splice(&dirty, dirty_page_list);
+	return left_dirty;
 }
 
 static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
@@ -388,6 +393,8 @@ void sgx_reclaim_direct(void)
 
 static int ksgxd(void *p)
 {
+	int left_dirty;
+
 	set_freezable();
 
 	/*
@@ -395,10 +402,10 @@ static int ksgxd(void *p)
 	 * required for SECS pages, whose child pages blocked EREMOVE.
 	 */
 	__sgx_sanitize_pages(&sgx_dirty_page_list);
-	__sgx_sanitize_pages(&sgx_dirty_page_list);
 
-	/* sanity check: */
-	WARN_ON(!list_empty(&sgx_dirty_page_list));
+	left_dirty = __sgx_sanitize_pages(&sgx_dirty_page_list);
+	if (left_dirty)
+		pr_warn("%d unsanitized pages\n", left_dirty);
 
 	while (!kthread_should_stop()) {
 		if (try_to_freeze())
-- 
2.37.1