[PATCH v2 6/7] x86/power: Sprinkle some noinstr

From: Peter Zijlstra <peterz@infradead.org>
To: x86@kernel.org, Joan Bruguera <joanbrugueram@gmail.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	"Juergen Gross" <jgross@suse.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	xen-devel <xen-devel@lists.xenproject.org>,
	"Jan Beulich" <jbeulich@suse.com>,
	"Roger Pau Monne" <roger.pau@citrix.com>,
	"Kees Cook" <keescook@chromium.org>,
	mark.rutland@arm.com, "Andrew Cooper" <Andrew.Cooper3@citrix.com>,
	"Jörg Rödel" <joro@8bytes.org>, "H. Peter Anvin" <hpa@zytor.com>
Subject: [PATCH v2 6/7] x86/power: Sprinkle some noinstr
Date: Mon, 16 Jan 2023 15:25:39 +0100	[thread overview]
Message-ID: <20230116143645.888786209@infradead.org> (raw)
In-Reply-To: 20230116142533.905102512@infradead.org

Ensure no compiler instrumentation sneaks in while restoring the CPU
state. Specifically we can't handle CALL/RET until GS is restored.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/power/cpu.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -192,7 +192,7 @@ static void fix_processor_context(void)
  * The asm code that gets us here will have restored a usable GDT, although
  * it will be pointing to the wrong alias.
  */
-static void notrace __restore_processor_state(struct saved_context *ctxt)
+static __always_inline void __restore_processor_state(struct saved_context *ctxt)
 {
 	struct cpuinfo_x86 *c;
 
@@ -235,6 +235,13 @@ static void notrace __restore_processor_
 	loadsegment(fs, __KERNEL_PERCPU);
 #endif
 
+	/*
+	 * Definitely wrong, but at this point we should have at least enough
+	 * to do CALL/RET (consider SKL callthunks) and this avoids having
+	 * to deal with the noinstr explosion for now :/
+	 */
+	instrumentation_begin();
+
 	/* Restore the TSS, RO GDT, LDT, and usermode-relevant MSRs. */
 	fix_processor_context();
 
@@ -276,10 +283,12 @@ static void notrace __restore_processor_
 	 * because some of the MSRs are "emulated" in microcode.
 	 */
 	msr_restore_context(ctxt);
+
+	instrumentation_end();
 }
 
 /* Needed by apm.c */
-void notrace restore_processor_state(void)
+void noinstr restore_processor_state(void)
 {
 	__restore_processor_state(&saved_context);
 }


