linux-kernel - Re: [PATCHv8 00/11] Linear Address Masking enabling

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Message-ID: <20220913000632.2o4alsekgskof2x2@box.shutemov.name>
Date:   Tue, 13 Sep 2022 03:06:32 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok_raj@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCHv8 00/11] Linear Address Masking enabling

On Mon, Sep 12, 2022 at 03:55:02PM -0700, Jacob Pan wrote:
> Hi Dave,
> 
> On Mon, 12 Sep 2022 14:41:56 -0700, Dave Hansen <dave.hansen@...el.com>
> wrote:
> 
> > On 9/12/22 13:39, Jacob Pan wrote:
> > >>> +	if (pasid_valid(mm->pasid) && !forced) {  
> > > I don't think this works since we have lazy pasid free.  for example,
> > > after all the devices did sva_unbind, mm->pasid  we'll remain valid
> > > until mmdrop(). LAM  should be supported in this case.  
> > 
> > Nah, it works fine.
> > It just means that the rules are "you can't do LAM if your process
> > *EVER* got a PASID" instead of "you can't do LAM if you are actively
> > using your PASID".
> Sure it works if you change the rules, but this case need to documented.
> 
> > 
> > We knew that PASID use would be a one-way trip for a process when we
> > moved to the simplified implementation.  This is just more fallout from
> > that.  It's fine.
> > 
> Is LAM also a one-way trip?

Yes.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov