linux-kernel - Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS

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Message-ID: <498F5590-2711-47E9-A58F-CC9EB41D71AA@zytor.com>
Date: Wed, 02 Jul 2025 10:10:58 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC: Sohil Mehta <sohil.mehta@...el.com>, Andy Lutomirski <luto@...nel.org>,
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Subject: Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS

On July 2, 2025 7:47:30 AM PDT, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:
>On Wed, Jul 02, 2025 at 07:37:12AM -0700, H. Peter Anvin wrote:
>> A LASS violation of any kind in the kernel (unless handled by fixup,
>> including user access fixup) ought to be fatal, correct?
>
>Yes, LASS violation is fatal for !user_mode(regs), unless addressed by
>fixups.
>
>For user_mode(regs), emulate_vsyscall_gp() is the notable exception.
>

Note also that for FRED we can have separate kernel and user space paths basically "for free". I'm not sure if we do that yet (if the infrastructure is there), but we could. 

Not that it matters for this case. This is a slow path.