Re: [PATCH 2/2] arm: Add ARM ERRATA 782773 workaround

[Simon Horman <horms@verge.net.au>]

On Thu, Sep 20, 2012 at 10:35:50AM +0100, Catalin Marinas wrote:
> On 13 September 2012 02:00, Simon Horman <horms@verge.net.au> wrote:
> > On Wed, Sep 12, 2012 at 10:59:35AM -0700, Stephen Boyd wrote:
> >> On 09/12/12 00:14, Simon Horman wrote:
> >> > @@ -1423,6 +1423,15 @@ config ARM_ERRATA_775420
> >> >           deadlock. This workaround puts DSB before executing ISB at the
> >> >           beginning of the abort exception handler.
> >> >
> >> > +config ARM_ERRATA_782773
> >> > +   bool "ARM errata: Updating a translation entry might cause an unexpected translation fault"
> >> > +   depends on CPU_V7
> >> > +   help
> >> > +     This option enables the workaround for the 782773 Cortex-A9 (all r0,
> >> > +     ,r2 and r3 revisions) erratum. It might cause MMU exception in case
> >>
> >> Seems to be an extra comma here.
> >
> > Thanks, here is an updated version.
> >
> > From: Kouei Abe <kouei.abe.cp@rms.renesas.com>
> >
> > arm: Add ARM ERRATA 782773 workaround
> >
> > Signed-off-by: Kouei Abe <kouei.abe.cp@rms.renesas.com>
> > Signed-off-by: Simon Horman <horms@verge.net.au>
> 
> I would add some text to the commit log as well, even though it
> matches the Kconfig entry.

Sure, an updated patch is below.
I also reworded the text to make it easier on my eyes,
I don't think the meaning has been altered.

> Have you hit this in practice? In general the kernel shouldn't access
> kernel virtual address corresponding to a page table that is being
> changed. For user address space it is possible but the kernel can
> handle use translation faults, even though they may be spurious.

I believe that Abe-san's team have come up against this,
I can confirm that if it is important.

----------------------------------------------------------------
From: Kouei Abe <kouei.abe.cp@rms.renesas.com>

arm: Add ARM ERRATA 782773 workaround

This is a workaround for Errata 782773 which effects all r0, r2 and r3
revisions.

The work-around avoids the possibility of an MMU exception in the case
where a page table walk occurs immediately after a page table update
that hasn't been flushed from the L1 data cache.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Kouei Abe <kouei.abe.cp@rms.renesas.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2
* Reword Kconfig description
* Add some details to changelog entry

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 48c19d4..2b76164 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1423,6 +1423,15 @@ config ARM_ERRATA_775420
 	 to deadlock. This workaround puts DSB before executing ISB if
 	 an abort may occur on cache maintenance.
 
+config ARM_ERRATA_782773
+	bool "ARM errata: Updating a translation entry might cause an unexpected translation fault"
+	depends on CPU_V7
+	help
+	  This option enables the workaround for the 782773 Cortex-A9 (all r0,
+	  r2 and r3 revisions) erratum. It might cause MMU exception in case
+	  page table walk happens just after updating the existing
+	  with setting page table in L1 data cache.
+
 endmenu
 
 source "arch/arm/common/Kconfig"
diff --git a/arch/arm/mm/proc-v7-2level.S b/arch/arm/mm/proc-v7-2level.S
index fd045e7..9207b9f 100644
--- a/arch/arm/mm/proc-v7-2level.S
+++ b/arch/arm/mm/proc-v7-2level.S
@@ -103,9 +103,17 @@ ENTRY(cpu_v7_set_pte_ext)
 	tstne	r1, #L_PTE_PRESENT
 	moveq	r3, #0
 
+#ifdef CONFIG_ARM_ERRATA_782773
+	mrs	r2, cpsr			@ save cpsr
+	cpsid	if				@ disable interrupts
+	mcr	p15, 0, r0, c7, c14, 1		@ clean & invalidate D line
+#endif
  ARM(	str	r3, [r0, #2048]! )
  THUMB(	add	r0, r0, #2048 )
  THUMB(	str	r3, [r0] )
+#ifdef CONFIG_ARM_ERRATA_782773
+	msr	cpsr_c, r2			@ load cpsr
+#endif
 	mcr	p15, 0, r0, c7, c10, 1		@ flush_pte
 #endif
 	mov	pc, lr
-- 
1.7.10.4