linux-kernel - Re: [PATCH] x86: Remove force

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Message-ID: <20191220193543.GD13464@redhat.com>
Date:   Fri, 20 Dec 2019 20:35:44 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Brian Gerst <brgerst@...il.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH] x86: Remove force_iret()

On 12/19, Brian Gerst wrote:
>
> force_iret() was originally intended to prevent the return to user mode with
> the SYSRET or SYSEXIT instructions, in cases where the register state could
> have been changed to be incompatible with those instructions.  The entry code
> has been significantly reworked since then, and register state is validated
> before SYSRET or SYSEXIT are used.  force_iret() no longer serves its original
> purpose and can be eliminated.

Plus iiuc today force_iret() == set_thread_flag(TIF_NOTIFY_RESUME) simply has
no effect on asm paths.

Acked-by: Oleg Nesterov <oleg@...hat.com>