linux-kernel - Re: Wake-up from suspend to RAM broken under `retbleed=stuff`

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Date:   Mon,  9 Jan 2023 04:05:31 +0000
From:   Joan Bruguera <joanbrugueram@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Wake-up from suspend to RAM broken under `retbleed=stuff`

This fixes wakeup for me on both QEMU and real HW
(just a proof of concept, don't merge)

diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index ffea98f9064b..8704bcc0ce32 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -7,6 +7,7 @@
 #include <linux/memory.h>
 #include <linux/moduleloader.h>
 #include <linux/static_call.h>
+#include <linux/suspend.h>
 
 #include <asm/alternative.h>
 #include <asm/asm-offsets.h>
@@ -150,6 +151,10 @@ static bool skip_addr(void *dest)
 	if (dest >= (void *)hypercall_page &&
 	    dest < (void*)hypercall_page + PAGE_SIZE)
 		return true;
+#endif
+#ifdef CONFIG_PM_SLEEP
+	if (dest == restore_processor_state)
+		return true;
 #endif
 	return false;
 }
diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index 236447ee9beb..e667894936f7 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -281,6 +281,9 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
 /* Needed by apm.c */
 void notrace restore_processor_state(void)
 {
+	/* Restore GS before calling anything to avoid crash on call depth accounting */
+	native_wrmsrl(MSR_GS_BASE, saved_context.kernelmode_gs_base);
+
 	__restore_processor_state(&saved_context);
 }
 #ifdef CONFIG_X86_32