linux-kernel - Re: [PATCH v8 11/12] arm64: entry: Convert to generic entry

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Message-ID: <65c7307b-1f4e-4ae7-8bcf-8bfd9a9186fb@arm.com>
Date: Mon, 1 Dec 2025 11:17:52 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>, catalin.marinas@....com,
 will@...nel.org, oleg@...hat.com, tglx@...utronix.de, peterz@...radead.org,
 luto@...nel.org, shuah@...nel.org, kees@...nel.org, wad@...omium.org,
 charlie@...osinc.com, akpm@...ux-foundation.org, ldv@...ace.io,
 macro@...am.me.uk, deller@....de, mark.rutland@....com, efault@....de,
 song@...nel.org, mbenes@...e.cz, ryan.roberts@....com,
 ada.coupriediaz@....com, anshuman.khandual@....com, broonie@...nel.org,
 pengcan@...inos.cn, dvyukov@...gle.com, kmal@...k.li,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v8 11/12] arm64: entry: Convert to generic entry

On 29/11/2025 02:23, Jinjie Ruan wrote:
>>>>>  #define TIF_UPROBE		5	/* uprobe breakpoint or singlestep */
>>>>>  #define TIF_MTE_ASYNC_FAULT	6	/* MTE Asynchronous Tag Check Fault */
>>>>>  #define TIF_NOTIFY_SIGNAL	7	/* signal notifications exist */
>>>>> -#define TIF_SYSCALL_TRACE	8	/* syscall trace active */
>>>>> -#define TIF_SYSCALL_AUDIT	9	/* syscall auditing */
>>>>> -#define TIF_SYSCALL_TRACEPOINT	10	/* syscall tracepoint for ftrace */
>>>>> -#define TIF_SECCOMP		11	/* syscall secure computing */
>>>>> -#define TIF_SYSCALL_EMU		12	/* syscall emulation active */
>>>>> +#define TIF_SECCOMP		11      /* syscall secure computing */
>>>>> +#define TIF_SYSCALL_EMU		12      /* syscall emulation active */
>>>> These seem to have reappeared in v8 for some reason?
>>> v8 add "ARCH_SYSCALL_WORK_EXIT" to be defined as "SECCOMP | SYSCALL_EMU"
>>>   to keep the arm64 behaviour unchanged as mentioned in v7.
>> Ah then that is where the issue is, I missed that: surely switching to
>> generic entry means that we are using SYSCALL_WORK_BIT_* rather than
>> TIF_* for all these flags?
> I think they may be the same thing as you mentioned in v7，neither
> SYSCALL_WORK_EXIT nor report_single_step() excluded SYSCALL_EMU, maybe
> we should clarify them for arm64 together in a separate patch.

These two might indeed be related. On second thoughts, while waiting for
more knowledgeable arm64 reviewers, I would suggest aligning arm64 with
the generic entry. Which means...

> 1、"The generic report_single_step() always returns false if SYSCALL_EMU
> is set."

... replicating this behaviour on arm64 (in a separate patch), and...

> 2、"
>      > -void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
>      > -{
>      > -	unsigned long flags = read_thread_flags();
>      > -
>      > -	rseq_syscall(regs);
>      > -
>      > -	if (has_syscall_work(flags) || flags & _TIF_SINGLESTEP)
>
>      I believe switching to the generic function introduces a change
>      here: syscall_exit_work() is only called if a flag in
> SYSCALL_WORK_EXIT is set, and this set does not include SYSCALL_EMU and
>     SECCOMP. Practically this means that audit_syscall_exit() will no
>     longer be called if only SECCOMP and/or SYSCALL_EMU is set.
>
>    It doesn't feel like a major behaviour change, but it should be
>    pointed out."

... replicating this on arm64 as well, i.e. introducing a separate set
of flags for syscall exit. This should be a patch of its own, as it
isn't directly related to the report_single_step() behaviour (especially
since it concerns SECCOMP as well). It would also be an occasion to get
rid of has_syscall_work(), in preparation to the move to generic entry.

- Kevin