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From: David Laight <David.Laight@ACULAB.COM>
Subject: RE: [PATCH 03/35] x86/entry/32: Load task stack from x86_tss.sp1 in
 SYSENTER handler
Date: Thu, 19 Apr 2018 09:01:12 +0000
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To: 'Andi Kleen' <ak@linux.intel.com>, Linus Torvalds <torvalds@linux-foundation.org>
Cc: Joerg Roedel <joro@8bytes.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>, the
 arch/x86 maintainers <x86@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, Andy
 Lutomirski <luto@kernel.org>, Dave Hansen <dave.hansen@intel.com>, Josh
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From: Andi Kleen
> Sent: 19 April 2018 01:39
>=20
> On Wed, Apr 18, 2018 at 05:02:02PM -0700, Linus Torvalds wrote:
> > On Wed, Apr 18, 2018 at 4:26 PM, Andi Kleen <ak@linux.intel.com> wrote:
> > >
> > > Seems like a hack. Why can't that be stored in a per cpu variable?
> >
> > It *is* a percpu variable - the whole x86_tss structure is percpu.
> >
> > I guess it could be a different (separate) percpu variable, but might
> > as well use the space we already have allocated.
>=20
> Would be better/cleaner to use a separate variable instead of reusing
> x86 structures like this. Who knows what subtle side effects that
> may have eventually.
>=20
> It will be also easier to understand in the code.

You could (probably) use an unnamed union in the x86_tss structure
so that it is more obvious that the two variables share a location.

	David