From mboxrd@z Thu Jan  1 00:00:00 1970
From: Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH v2 04/19] arm64: mte: Use Normal Tagged attributes for
 the linear map
Date: Thu, 5 Mar 2020 16:38:10 +0000
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To: Steven Price <steven.price@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, Richard Earnshaw <Richard.Earnshaw@arm.com>, Szabolcs Nagy <szabolcs.nagy@arm.com>, Andrey Konovalov <andreyknvl@google.com>, Kevin Brodsky <kevin.brodsky@arm.com>, Peter Collingbourne <pcc@google.com>, linux-mm@kvack.org, Vincenzo Frascino <vincenzo.frascino@arm.com>, Will Deacon <will@kernel.org>

On Thu, Mar 05, 2020 at 04:21:34PM +0000, Steven Price wrote:
> On 26/02/2020 18:05, Catalin Marinas wrote:
> > +	if (system_supports_mte()) {
> > +		/*
> > +		 * Changing the memory type between Normal and Normal-Tagged
> > +		 * is safe since Tagged is considered a permission attribute
> > +		 * from the mismatched attribute aliases perspective.
> > +		 */
> > +		if ((old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
> > +		    (old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED) ||
> > +		    (new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
> > +		    (new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED))
> > +			mask |= PTE_ATTRINDX_MASK;
> > +	}
> > +
> >  	return ((old ^ new) & ~mask) == 0;
> >  }
> 
> This is much more permissive than I would expect. If either the old or
> new memory type is NORMAL (or NORMAL_TAGGED) then the memory type is
> ignored altogether.
> 
> Should this check be:
> 
> if (((old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
>      (old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED)) &&
>     ((new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
>      (new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED)))

You are right, I think my patch allows many other memory type
combinations. Thanks.

-- 
Catalin