linux-kernel - [tip: x86/fpu] x86/fpu: Delay instruction pointer fixup until after warning

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Message-ID: <175089453700.406.1518104364215542733.tip-bot2@tip-bot2>
Date: Wed, 25 Jun 2025 23:35:36 -0000
From: "tip-bot2 for Dave Hansen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, Chao Gao <chao.gao@...el.com>,
 Alison Schofield <alison.schofield@...el.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, stable@...r.kernel.org,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: x86/fpu] x86/fpu: Delay instruction pointer fixup until after warning

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     1cec9ac2d071cfd2da562241aab0ef701355762a
Gitweb:        https://git.kernel.org/tip/1cec9ac2d071cfd2da562241aab0ef701355762a
Author:        Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate:    Tue, 24 Jun 2025 14:01:48 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Wed, 25 Jun 2025 16:28:06 -07:00

x86/fpu: Delay instruction pointer fixup until after warning

Right now, if XRSTOR fails a console message like this is be printed:

	Bad FPU state detected at restore_fpregs_from_fpstate+0x9a/0x170, reinitializing FPU registers.

However, the text location (...+0x9a in this case) is the instruction
*AFTER* the XRSTOR. The highlighted instruction in the "Code:" dump
also points one instruction late.

The reason is that the "fixup" moves RIP up to pass the bad XRSTOR and
keep on running after returning from the #GP handler. But it does this
fixup before warning.

The resulting warning output is nonsensical because it looks like the
non-FPU-related instruction is #GP'ing.

Do not fix up RIP until after printing the warning. Do this by using
the more generic and standard ex_handler_default().

Fixes: d5c8028b4788 ("x86/fpu: Reinitialize FPU registers if restoring FPU state fails")
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Chao Gao <chao.gao@...el.com>
Acked-by: Alison Schofield <alison.schofield@...el.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc:stable@...r.kernel.org
Link: https://lore.kernel.org/all/20250624210148.97126F9E%40davehans-spike.ostc.intel.com
---
 arch/x86/mm/extable.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index bf8dab1..2fdc1f1 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -122,13 +122,12 @@ static bool ex_handler_sgx(const struct exception_table_entry *fixup,
 static bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 				 struct pt_regs *regs)
 {
-	regs->ip = ex_fixup_addr(fixup);
-
 	WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
 		  (void *)instruction_pointer(regs));
 
 	fpu_reset_from_exception_fixup();
-	return true;
+
+	return ex_handler_default(fixup, regs);
 }
 
 /*