linux-kernel - Re: [PATCH v4 04/11] kernel/fork: Initialize mm's PASID

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Date:   Mon, 14 Feb 2022 18:23:54 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>
Cc:     iommu@...ts.linux-foundation.org, x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v4 04/11] kernel/fork: Initialize mm's PASID

On Mon, Feb 07 2022 at 15:02, Fenghua Yu wrote:

> A new mm doesn't have a PASID yet when it's created. Initialize
> the mm's PASID on fork() or for init_mm to INVALID_IOASID (-1).
>
> INIT_PASID (0) is reserved for kernel legacy DMA PASID. It cannot be
> allocated to a user process. Initializing the process's PASID to 0 may
> cause confusion that why the process uses the reserved kernel legacy DMA
> PASID. Initializing the PASID to INVALID_IOASID (-1) explicitly
> tells the process doesn't have a valid PASID yet.
>
> Even though the only user of mm_pasid_init() is in fork.c, define it
> in <linux/sched/mm.h> as the first of three mm/pasid life cycle
> functions (init/set/drop) to keep these all together.
>
> Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>