linux-kernel - Re: [PATCH v6 01/12] iommu: Change type of pasid to u32

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Date:   Tue, 14 Jul 2020 06:54:49 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        H Peter Anvin <hpa@...or.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        amd-gfx <amd-gfx@...ts.freedesktop.org>
Subject: Re: [PATCH v6 01/12] iommu: Change type of pasid to u32

On Mon, Jul 13, 2020 at 07:45:49PM -0700, Liu, Yi L wrote:
> > From: Fenghua Yu <fenghua.yu@...el.com>
> > Sent: Tuesday, July 14, 2020 7:48 AM
> >
> > PASID is defined as a few different types in iommu including "int",
> > "u32", and "unsigned int". To be consistent and to match with uapi
> > definitions, define PASID and its variations (e.g. max PASID) as "u32".
> > "u32" is also shorter and a little more explicit than "unsigned int".
> >
> > No PASID type change in uapi although it defines PASID as __u64 in
> > some places.
> 
> just out of curious, why not using ioasid_t? In Linux kernel, PASID is
> managed by ioasid.

ioasid_t is only used in limited underneath files (ioasid.c and ioasid.h).
Instead of changing hundreds of places to use ioasid_t, it's better to
keep ioasid_t only used in the files.

And it's explict and matches with uapi to define PASID as u32. Changing
to ioasid_t in so many files (amd, gpu, crypto, etc) may confuse upper
users on "why ioasid_t".

So we had better to explicitly define PASID as u32 and keep ioasid_t in
the limited underneath files.

Thanks.

-Fenghua