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Re: [PATCH v4 03/12] target/arm: Fix mte_checkN

From: Peter Maydell
Subject: Re: [PATCH v4 03/12] target/arm: Fix mte_checkN
Date: Thu, 8 Apr 2021 08:50:36 +0000

On Wed, 7 Apr 2021 at 19:54, Alex Bennée <alex.bennee@linaro.org> wrote:
> Richard Henderson <richard.henderson@linaro.org> writes:
> > We were incorrectly assuming that only the first byte of an MTE access
> > is checked against the tags.  But per the ARM, unaligned accesses are
> > pre-decomposed into single-byte accesses.  So by the time we reach the
> > actual MTE check in the ARM pseudocode, all accesses are aligned.
> >
> > Therefore, the first failure is always either the first byte of the
> > access, or the first byte of the granule.
> >
> > In addition, some of the arithmetic is off for last-first -> count.
> > This does not become directly visible until a later patch that passes
> > single bytes into this function, so ptr == ptr_last.
> >
> > Buglink: https://bugs.launchpad.net/bugs/1921948
> Minor note: you can Cc: Bug 1921948 <1921948@bugs.launchpad.net> to
> automatically copy patches to the appropriate bugs which is useful if
> you don't have the Cc for the reporter.

I'm not sure cc'ing bugs on patches is very useful, though (and especially
not for big series). I usually prefer to just add a note to the bug with
the URL of the series in patchew afterwards.

-- PMM

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