[PATCH v2 14/28] arm64/sve: Backend logic for setting the vector length

[Dave Martin]

On Wed, Sep 13, 2017 at 03:11:23PM -0700, Catalin Marinas wrote:
> On Wed, Sep 13, 2017 at 08:06:12PM +0100, Dave P Martin wrote:
> > On Wed, Sep 13, 2017 at 10:29:11AM -0700, Catalin Marinas wrote:
> > > On Thu, Aug 31, 2017 at 06:00:46PM +0100, Dave P Martin wrote:
> > > > This patch implements the core logic for changing a task's vector
> > > > length on request from userspace.  This will be used by the ptrace
> > > > and prctl frontends that are implemented in later patches.
> > > > 
> > > > The SVE architecture permits, but does not require, implementations
> > > > to support vector lengths that are not a power of two.  To handle
> > > > this, logic is added to check a requested vector length against a
> > > > possibly sparse bitmap of available vector lengths at runtime, so
> > > > that the best supported value can be chosen.
> > > > 
> > > > Signed-off-by: Dave Martin <Dave.Martin at arm.com>
> > > > Cc: Alex Bennée <alex.bennee at linaro.org>
> > > 
> > > Can this be merged with patch 20? It seems to add the PR_ definitions
> > > which get actually used later when the prctl interface is added.
> > 
> > This patch is used both by patch 19 and by patch 20, which I preferred
> > not to merge with each other: ptrace and prctl are significantly
> > different things.
> > 
> > The prctl bit definitions are added here because they are the canonical
> > definitions used by both interfaces.  The ptrace #defines are based on
> > them.
> > 
> > Does it make sense if I merge patch 20 into this one and apply patch 19
> > on top?  This avoide the appearance of prctl #defines with no prctl
> > implementation.
> 
> That's fine, you can bring patch 20 forward. If there are other
> non-trivial issues, feel free to ignore my comment.

I've had a go at this, but I think it's going to be more trouble than
it's worth -- there are other interdependencies between the patches
which make them tricky to reorder.

I could add a note in the commit message for this patch explaining why
the prctl flag #defines are being added here.  What do you think?

Cheers
---Dave