[PATCH 3.2 076/115] parisc: Unbreak handling exceptions from kernel modules

[Ben Hutchings]

3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Helge Deller <del...@gmx.de>

commit 2ef4dfd9d9f288943e249b78365a69e3ea3ec072 upstream.

Handling exceptions from modules never worked on parisc.
It was just masked by the fact that exceptions from modules
don't happen during normal use.

When a module triggers an exception in get_user() we need to load the
main kernel dp value before accessing the exception_data structure, and
afterwards restore the original dp value of the module on exit.

Noticed-by: Mikulas Patocka <mpato...@redhat.com>
Signed-off-by: Helge Deller <del...@gmx.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 arch/parisc/include/asm/uaccess.h | 1 +
 arch/parisc/kernel/asm-offsets.c  | 1 +
 arch/parisc/lib/fixup.S           | 6 ++++++
 arch/parisc/mm/fault.c            | 1 +
 4 files changed, 9 insertions(+)

--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -79,6 +79,7 @@ struct exception_table_entry {
  */
 struct exception_data {
        unsigned long fault_ip;
+       unsigned long fault_gp;
        unsigned long fault_space;
        unsigned long fault_addr;
 };
--- a/arch/parisc/kernel/asm-offsets.c
+++ b/arch/parisc/kernel/asm-offsets.c
@@ -292,6 +292,7 @@ int main(void)
        DEFINE(ASM_PT_INITIAL, PT_INITIAL);
        BLANK();
        DEFINE(EXCDATA_IP, offsetof(struct exception_data, fault_ip));
+       DEFINE(EXCDATA_GP, offsetof(struct exception_data, fault_gp));
        DEFINE(EXCDATA_SPACE, offsetof(struct exception_data, fault_space));
        DEFINE(EXCDATA_ADDR, offsetof(struct exception_data, fault_addr));
        BLANK();
--- a/arch/parisc/lib/fixup.S
+++ b/arch/parisc/lib/fixup.S
@@ -26,6 +26,7 @@
 
 #ifdef CONFIG_SMP
        .macro  get_fault_ip t1 t2
+       loadgp
        addil LT%__per_cpu_offset,%r27
        LDREG RT%__per_cpu_offset(%r1),\t1
        /* t2 = smp_processor_id() */
@@ -40,14 +41,19 @@
        LDREG RT%exception_data(%r1),\t1
        /* t1 = &__get_cpu_var(exception_data) */
        add,l \t1,\t2,\t1
+       /* %r27 = t1->fault_gp - restore gp */
+       LDREG EXCDATA_GP(\t1), %r27
        /* t1 = t1->fault_ip */
        LDREG EXCDATA_IP(\t1), \t1
        .endm
 #else
        .macro  get_fault_ip t1 t2
+       loadgp
        /* t1 = &__get_cpu_var(exception_data) */
        addil LT%exception_data,%r27
        LDREG RT%exception_data(%r1),\t2
+       /* %r27 = t2->fault_gp - restore gp */
+       LDREG EXCDATA_GP(\t2), %r27
        /* t1 = t2->fault_ip */
        LDREG EXCDATA_IP(\t2), \t1
        .endm
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -147,6 +147,7 @@ int fixup_exception(struct pt_regs *regs
                struct exception_data *d;
                d = &__get_cpu_var(exception_data);
                d->fault_ip = regs->iaoq[0];
+               d->fault_gp = regs->gr[27];
                d->fault_space = regs->isr;
                d->fault_addr = regs->ior;