linux-kernel - Re: arch_set_user_pkey_access only works on the current task

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Message-ID: <774b6e6c8cb1be4923048bb1bb18753a6854758f.camel@pku.edu.cn>
Date:   Tue, 08 Jun 2021 11:16:53 +0800
From:   liangjs <liangjs@....edu.cn>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: arch_set_user_pkey_access only works on the current task_struct

On Mon, 2021-06-07 at 10:52 -0700, Dave Hansen wrote:
> On 6/5/21 6:10 AM, Jiashuo Liang wrote:
> > I am learning the kernel implementation of the x86 PKU feature. I find the
> > arch_set_user_pkey_access function in arch/x86/kernel/fpu/xstate.c does not
> > use its first parameter. So it is perhaps a bug?
> 
> I wouldn't really call it a bug.  But, yes, it is something we should
> clean up.

Should we remove the tsk parameter, or allow it to change the PKRU of tsk?

By the way, we are calling write_pkru, which changes both the CPU's PKRU
and the xsave one. Why is this necessary?

If I want to change PKRU of a task_struct other than current, do I still
need to call __write_pkru?

Thank you!
liangjs