Re: [PATCH 3.2 12/24] MIPS: Fix C0_Pagegrain[IEC] support.

From: David Daney
Date: Tue Mar 03 2015 - 18:24:40 EST

On 03/03/2015 02:11 PM, Ben Hutchings wrote:
3.2.68-rc1 review patch. If anyone has any objections, please let me know.

I object!

Because ...


From: David Daney <david.daney@xxxxxxxxxx>

commit 9ead8632bbf454cfc709b6205dc9cd8582fb0d64 upstream.

The following commits:

5890f70f15c52d (MIPS: Use dedicated exception handler if CPU supports RI/XI exceptions)
6575b1d4173eae (MIPS: kernel: cpu-probe: Detect unique RI/XI exceptions)

break the kernel for *all* existing MIPS CPUs that implement the
CP0_PageGrain[IEC] bit. They cause the TLB exception handlers to be
generated without the legacy execute-inhibit handling, but never set
the CP0_PageGrain[IEC] bit to activate the use of dedicated exception
vectors for execute-inhibit exceptions. The result is that upon
detection of an execute-inhibit violation, we loop forever in the TLB
exception handlers instead of sending SIGSEGV to the task.

If we are generating TLB exception handlers expecting separate
vectors, we must also enable the CP0_PageGrain[IEC] feature.

The bug was introduced in kernel version 3.17.

... I don't think the patch should be applied to versions prior to 3.17

David Daney

Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
Cc: Leonid Yegoshin <Leonid.Yegoshin@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
arch/mips/mm/tlb-r4k.c | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/mips/mm/tlb-r4k.c
+++ b/arch/mips/mm/tlb-r4k.c
@@ -447,6 +447,8 @@ void __cpuinit tlb_init(void)
#ifdef CONFIG_64BIT
pg |= PG_ELPA;
+ if (cpu_has_rixiex)
+ pg |= PG_IEC;

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