linux-kernel - Re: [PATCH v4 0/2] x86/fred: Prevent single-step upon ERETU completion

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Message-ID: <06e68373-a92b-472e-8fd9-ba548119770c@intel.com>
Date: Thu, 5 Jun 2025 14:51:43 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Xin Li (Intel)" <xin@...or.com>, <linux-kernel@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>
CC: <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<shuah@...nel.org>, <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v4 0/2] x86/fred: Prevent single-step upon ERETU
 completion

On 6/5/2025 12:32 PM, Sohil Mehta wrote:
> On 6/5/2025 11:10 AM, Xin Li (Intel) wrote:
> 
>>
>> Xin Li (Intel) (2):
>>   x86/fred/signal: Prevent single-step upon ERETU completion
>>   selftests/x86: Add a test to detect infinite sigtrap handler loop
>>
> 
> I tested the patches on a machine that supports FRED. The results are as
> expected:
> 

Seeing a split lock warning when running the test:
x86/split lock detection: #DB: sigtrap_loop_64/4614 took a bus_lock trap
at address: 0x4011ae

Wanted to get this out sooner for awareness. Will figure out more
details and send out an update.

> FRED on  — no Fix   => FAIL
> FRED off — no Fix   => PASS
> FRED on  — with Fix => PASS
> FRED off — with Fix => PASS
> 
> Tested-by: Sohil Mehta <sohil.mehta@...el.com>
> 
> Though, I haven't tested the 32-bit version of the selftest.
> 
>>  arch/x86/include/asm/sighandling.h         | 22 +++++
>>  arch/x86/kernel/signal_32.c                |  4 +
>>  arch/x86/kernel/signal_64.c                |  4 +
>>  tools/testing/selftests/x86/Makefile       |  2 +-
>>  tools/testing/selftests/x86/sigtrap_loop.c | 97 ++++++++++++++++++++++
>>  5 files changed, 128 insertions(+), 1 deletion(-)
>>  create mode 100644 tools/testing/selftests/x86/sigtrap_loop.c
>>