From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 2 Sep 2020 13:25:52 +0000 (+0200)
Subject: x86/debug: Sync BTF earlier
X-Git-Tag: Ubuntu-5.13.0-19.19~4927^2~10
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=c182487da1b5281463f2255d2347885dba219c08;p=mirror_ubuntu-jammy-kernel.git

x86/debug: Sync BTF earlier

Move the BTF sync near the DR6 load, as this will be the only common
code guaranteed to run on every #DB.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200902133200.786888252@infradead.org
---

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 81a2fb711091..99456428fb98 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -749,6 +749,13 @@ static __always_inline unsigned long debug_read_clear_dr6(void)
 	/* Filter out all the reserved bits which are preset to 1 */
 	dr6 &= ~DR6_RESERVED;
 
+	/*
+	 * The SDM says "The processor clears the BTF flag when it
+	 * generates a debug exception."  Clear TIF_BLOCKSTEP to keep
+	 * TIF_BLOCKSTEP in sync with the hardware BTF flag.
+	 */
+	clear_thread_flag(TIF_BLOCKSTEP);
+
 	return dr6;
 }
 
@@ -782,13 +789,6 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6, bool user)
 	bool user_icebp;
 	int si_code;
 
-	/*
-	 * The SDM says "The processor clears the BTF flag when it
-	 * generates a debug exception."  Clear TIF_BLOCKSTEP to keep
-	 * TIF_BLOCKSTEP in sync with the hardware BTF flag.
-	 */
-	clear_thread_flag(TIF_BLOCKSTEP);
-
 	/*
 	 * If DR6 is zero, no point in trying to handle it. The kernel is
 	 * not using INT1.