linux-kernel - Re: [linus:master] [x86/entry] be5341eb0d: WARNING:CPU:#PID:#at_int80

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Date: Wed, 20 Dec 2023 15:39:40 -0800
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Linus Torvalds <torvalds@...uxfoundation.org>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>, Borislav Petkov <bp@...en8.de>, 
	kernel test robot <oliver.sang@...el.com>, Thomas Gleixner <tglx@...utronix.de>, oe-lkp@...ts.linux.dev, 
	lkp@...el.com, linux-kernel@...r.kernel.org, 
	Dave Hansen <dave.hansen@...ux.intel.com>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, xen-devel@...ts.xenproject.org
Subject: Re: [linus:master] [x86/entry] be5341eb0d: WARNING:CPU:#PID:#at_int80_emulation

On Tue, Dec 19, 2023 at 3:15 PM Linus Torvalds
<torvalds@...uxfoundation.org> wrote:
>
> On Tue, 19 Dec 2023 at 12:17, Linus Torvalds
> <torvalds@...uxfoundation.org> wrote:
> >
> > That said, I still think that just getting rid of this horrid special
> > case for posix timers is the right thing, and we should just remove
> > that SYS_NI() alias thing entirely.
>
> IOW, something like the attached patch.
>
> It's not extensively tested, but hey, the diffstat looks nice:
>
>   arch/arm64/include/asm/syscall_wrapper.h |  4 ---
>   arch/riscv/include/asm/syscall_wrapper.h |  5 ----
>   arch/s390/include/asm/syscall_wrapper.h  | 13 +--------
>   arch/x86/include/asm/syscall_wrapper.h   | 34 +++---------------------
>   kernel/sys_ni.c                          | 14 ++++++++++
>   kernel/time/posix-stubs.c                | 45 --------------------------------
>   6 files changed, 19 insertions(+), 96 deletions(-)
>
> and it builds in at least a *couple* of configurations, including with
> CONFIG_POSIX_TIMERS disabled.
>
> I did *not* check whether it might fix the warning, since I doubt my
> user space would even boot without that posix timer support (actually,
> honestly, because I'm just lazy and "it _looks_ fine to me" was the
> main real thing).

I tested the patch with the 0-day bot reproducer and it does fix the
warning. My usual arm64 and riscv configs also seem to build and boot
just fine.

> But that SYS_NI() thing really does deserve to die, as it was purely
> used as a hack for some random timer system calls.
>
> Comments?

Removing the SYS_NI bits is definitely a cleaner solution. Looks good to me.

Reviewed-by: Sami Tolvanen <samitolvanen@...gle.com>
Tested-by: Sami Tolvanen <samitolvanen@...gle.com>

Sami