linux-kernel - Re: [PATCH v2 1/1] x86/fred/signal: Prevent single-step upon ERETU completion

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Message-ID: <3D4D48D6-D6E7-4391-8DCF-6B9D307FE2E2@zytor.com>
Date: Thu, 22 May 2025 14:28:33 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Andrew Cooper <andrew.cooper3@...rix.com>,
        Dave Hansen <dave.hansen@...el.com>, "Xin Li (Intel)" <xin@...or.com>,
        linux-kernel@...r.kernel.org
CC: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, peterz@...radead.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/1] x86/fred/signal: Prevent single-step upon ERETU completion

On May 22, 2025 10:53:16 AM PDT, Andrew Cooper <andrew.cooper3@...rix.com> wrote:
>On 22/05/2025 6:22 pm, Dave Hansen wrote:
>> On 5/22/25 10:17, Xin Li (Intel) wrote:
>>> Clear the software event flag in the augmented SS to prevent infinite
>>> SIGTRAP handler loop if TF is used without an external debugger.
>> Do you have a test case for this? It seems like the kind of thing we'd
>> want in selftests/.
>
>Hmm.
>
>This was a behaviour intentionally changed in FRED so traps wouldn't get
>lost if an exception where to occur.
>
>What precise case is triggering this?
>
>~Andrew

SIGTRAP → sigreturn. Basically, we have to uplevel the suppression behavior to the kernel (where it belongs) instead of doing it at the ISA level.