Date:   Mon, 20 Feb 2023 19:22:18 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     KP Singh <kpsingh@kernel.org>
Cc:     Josh Poimboeuf <jpoimboe@kernel.org>, linux-kernel@vger.kernel.org,
        pjt@google.com, evn@google.com, tglx@linutronix.de,
        mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org,
        hpa@zytor.com, peterz@infradead.org,
        pawan.kumar.gupta@linux.intel.com, kim.phillips@amd.com,
        alexandre.chartre@oracle.com, daniel.sneddon@linux.intel.com,
        =?utf-8?B?Sm9zw6k=?= Oliveira <joseloliveira11@gmail.com>,
        Rodrigo Branco <rodrigo@kernelhacking.com>,
        Alexandra Sandulescu <aesa@google.com>,
        Jim Mattson <jmattson@google.com>, stable@vger.kernel.org
Subject: Re: [PATCH RESEND] x86/speculation: Fix user-mode spectre-v2
 protection with KERNEL_IBRS
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On Mon, Feb 20, 2023 at 10:01:57AM -0800, KP Singh wrote:
> Well, we disable IBRS userspace (this is KENREL_IBRS), because it is
> slow. Now if a user space process wants to protect itself from cross
> thread training, it should be able to do it, either by turning STIBP
> always on or using a prctl to enable. With the current logic, it's
> unable to do so.

Ofcourse it can:

	[SPECTRE_V2_USER_PRCTL]                 = "User space: Mitigation: STIBP via prctl",

we did this at the time so that a userspace process can control it via
prctl().

So, maybe you should explain what you're trying to accomplish in detail
and where it fails...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette