linux-kernel - Re: [RFC PATCH 4/6] ARM: Remove __ARCH_WANT_INTERRUPTS_ON

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Date:	Thu, 1 Dec 2011 09:26:39 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Frank Rowand <frank.rowand@...sony.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [RFC PATCH 4/6] ARM: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW on
 ASID-capable CPUs

On Thu, Dec 01, 2011 at 02:57:07AM +0000, Frank Rowand wrote:
> On 11/29/11 04:22, Catalin Marinas wrote:
> > Since the ASIDs must be unique to an mm across all the CPUs in a system,
> > the __new_context() function needs to broadcast a context reset event to
> > all the CPUs during ASID allocation if a roll-over occurred. Such IPIs
> > cannot be issued with interrupts disabled and ARM had to define
> > __ARCH_WANT_INTERRUPTS_ON_CTXSW.
> > 
> > This patch changes the check_context() function to
> > check_and_switch_context() called from switch_mm(). In case of
> > ASID-capable CPUs (ARMv6 onwards), if a new ASID is needed, it defers
> > the __new_context() and cpu_switch_mm() calls to the post-lock switch
> > hook where the interrupts are enabled. Setting the reserved TTBR0 was
> > also moved to check_and_switch_context() from cpu_v7_switch_mm().
> > 
> > Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> > Cc: Russell King <linux@....linux.org.uk>
> > ---
> >  arch/arm/include/asm/mmu_context.h |   81 ++++++++++++++++++++++++++++--------
> >  arch/arm/include/asm/system.h      |    2 +
> >  arch/arm/include/asm/thread_info.h |    1 +
> >  arch/arm/mm/context.c              |    4 +-
> >  arch/arm/mm/proc-v7.S              |    3 -
> >  5 files changed, 69 insertions(+), 22 deletions(-)
> > 
> 
> < snip >
> 
> > diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
> > index 2faff3b..d5334d9 100644
> > --- a/arch/arm/mm/proc-v7.S
> > +++ b/arch/arm/mm/proc-v7.S
> > @@ -116,9 +116,6 @@ ENTRY(cpu_v7_switch_mm)
> >  #ifdef CONFIG_ARM_ERRATA_430973
> >  	mcr	p15, 0, r2, c7, c5, 6		@ flush BTAC/BTB
> >  #endif
> > -	mrc	p15, 0, r2, c2, c0, 1		@ load TTB 1
> > -	mcr	p15, 0, r2, c2, c0, 0		@ into TTB 0
> > -	isb
> >  #ifdef CONFIG_ARM_ERRATA_754322
> >  	dsb
> >  #endif
> 
> I do not have a tree that matches this version of cpu_v7_switch_mm().
> Can you point me at a tree that I can see this in?

That's added by the second patch in the series (and removed in a later
patch but it is a logical change in both situations and keeps the code
bisectable).

-- 
Catalin
--
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