linux-kernel - [PATCH] x86/sev: Disable ftrace branch profiling in SEV startup code

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Message-ID: <20250107151826.820147-2-ardb+git@google.com>
Date: Tue,  7 Jan 2025 16:18:27 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>, Tom Lendacky <thomas.lendacky@....com>, 
	kernel test robot <lkp@...el.com>
Subject: [PATCH] x86/sev: Disable ftrace branch profiling in SEV startup code

From: Ard Biesheuvel <ardb@...nel.org>

Ftrace branch profiling inserts absolute references to its metadata at
call sites, and this implies that this kind of instrumentation cannot be
used while executing from the 1:1 mapping of memory.

Therefore, disable ftrace branch profiling in the SEV startup routines,
by disabling it for the entire SEV core source file.

Cc: Tom Lendacky <thomas.lendacky@....com>
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501072244.zZrx9864-lkp@intel.com/
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/coco/sev/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 86898547056e..b5c6c4afd1cc 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -9,6 +9,8 @@
 
 #define pr_fmt(fmt)	"SEV: " fmt
 
+#define DISABLE_BRANCH_PROFILING
+
 #include <linux/sched/debug.h>	/* For show_regs() */
 #include <linux/percpu-defs.h>
 #include <linux/cc_platform.h>
-- 
2.47.1.613.gc27f4b7a9f-goog