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

[Thomas Gleixner]

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@xxxxxxxxxxxxxxx>
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>

Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>