linux-kernel - [RFC][PATCH 5/6] PM / hibernate: Add minimal noinstr annotations

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Message-ID: <20230112143825.822328168@infradead.org>
Date:   Thu, 12 Jan 2023 15:31:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, Joan Bruguera <joanbrugueram@...il.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        Juergen Gross <jgross@...e.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Jan Beulich <jbeulich@...e.com>,
        Roger Pau Monne <roger.pau@...rix.com>,
        Kees Cook <keescook@...omium.org>, mark.rutland@....com
Subject: [RFC][PATCH 5/6] PM / hibernate: Add minimal noinstr annotations

When resuming there must not be any code between swsusp_arch_suspend()
and restore_processor_state() since the CPU state is ill defined at
this point in time.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/power/hibernate.c |   30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -280,6 +280,32 @@ __weak int arch_resume_nosmt(void)
 	return 0;
 }
 
+static noinstr int suspend_and_restore(void)
+{
+	int error;
+
+	/*
+	 * Strictly speaking swsusp_arch_suspend() should be noinstr too but it
+	 * is typically written in asm, as such, assume it is good and shut up
+	 * the validator.
+	 */
+	instrumentation_begin();
+	error = swsusp_arch_suspend();
+	instrumentation_end();
+
+	/*
+	 * Architecture resume code 'returns' from the swsusp_arch_suspend()
+	 * call and resumes execution here with some very dodgy machine state.
+	 *
+	 * Compiler instrumentation between these two calls (or in
+	 * restore_processor_state() for that matter) will make life *very*
+	 * interesting indeed.
+	 */
+	restore_processor_state();
+
+	return error;
+}
+
 /**
  * create_image - Create a hibernation image.
  * @platform_mode: Whether or not to use the platform driver.
@@ -323,9 +349,7 @@ static int create_image(int platform_mod
 	in_suspend = 1;
 	save_processor_state();
 	trace_suspend_resume(TPS("machine_suspend"), PM_EVENT_HIBERNATE, true);
-	error = swsusp_arch_suspend();
-	/* Restore control flow magically appears here */
-	restore_processor_state();
+	error = suspend_and_restore();
 	trace_suspend_resume(TPS("machine_suspend"), PM_EVENT_HIBERNATE, false);
 	if (error)
 		pr_err("Error %d creating image\n", error);