[ORLinux] [RFC PATCH] openrisc/mm: move protection fault detection to do_page

Stefan Kristiansson

2013-07-31 19:58:00 UTC

Instead of clearing the 'vector' parameter to do_page_fault()
to indicate that a fault was caused by a non-protection error,
make do_page_fault figure this out on its own.

This is done by peeking into the TLBs to see if the page that
caused the fault is not cached in any of the TLB entries
(i.e. a TLB miss).
This works, because only a page fault generated at the same time
as a TLB hit can be a protection fault, and vice versa.

The motivation for this is that, the 'vector' parameter is
cleared by the TLB miss exceeption vectors, but in order to
support hardware page walks (which are supported by the
architecture) one can not rely on the non-protective
page fault coming through the TLB miss vectors.

Signed-off-by: Stefan Kristiansson <stefan.kristiansson at saunalahti.fi>
---
So, this is my take on solving the problem presented in the
"Hardware assisted tlb reload in mor1kx" thread, where the tlb miss
handlers are passing information to do_page_fault() .
It was the cleanest solution I could come up with that emulates
the previous behaviour, but there could be some better way to solve
this on a "higher" level that surpasses my understanding of the
Linux mm system.

---
arch/openrisc/kernel/entry.S | 12 ------------
arch/openrisc/kernel/head.S | 4 ++--
arch/openrisc/mm/fault.c | 42 +++++++++++++++++++++++++++++++++++++-----
3 files changed, 39 insertions(+), 19 deletions(-)

diff --git a/arch/openrisc/kernel/entry.S b/arch/openrisc/kernel/entry.S
index 46d42b8..f6b923f 100644
--- a/arch/openrisc/kernel/entry.S
+++ b/arch/openrisc/kernel/entry.S
@@ -201,15 +201,9 @@ EXCEPTION_ENTRY(_bus_fault_handler)
l.nop

/* ---[ 0x300: Data Page Fault exception ]------------------------------- */
-EXCEPTION_ENTRY(_dtlb_miss_page_fault_handler)
- l.and r5,r5,r0
- l.j 1f
- l.nop
-
EXCEPTION_ENTRY(_data_page_fault_handler)
/* set up parameters for do_page_fault */
l.ori r5,r0,0x300 // exception vector
-1:
l.addi r3,r1,0 // pt_regs
/* r4 set be EXCEPTION_HANDLE */ // effective address of fault

@@ -281,15 +275,9 @@ EXCEPTION_ENTRY(_data_page_fault_handler)
l.nop

/* ---[ 0x400: Insn Page Fault exception ]------------------------------- */
-EXCEPTION_ENTRY(_itlb_miss_page_fault_handler)
- l.and r5,r5,r0
- l.j 1f
- l.nop
-
EXCEPTION_ENTRY(_insn_page_fault_handler)
/* set up parameters for do_page_fault */
l.ori r5,r0,0x400 // exception vector
-1:
l.addi r3,r1,0 // pt_regs
/* r4 set be EXCEPTION_HANDLE */ // effective address of fault
l.ori r6,r0,0x0 // !write access
diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
index 1d3c9c2..5ebd37a 100644
--- a/arch/openrisc/kernel/head.S
+++ b/arch/openrisc/kernel/head.S
@@ -1070,7 +1070,7 @@ d_pte_not_present:
EXCEPTION_LOAD_GPR4
EXCEPTION_LOAD_GPR5
EXCEPTION_LOAD_GPR6
- EXCEPTION_HANDLE(_dtlb_miss_page_fault_handler)
+ EXCEPTION_HANDLE(_data_page_fault_handler)

/* ==============================================[ ITLB miss handler ]=== */
ENTRY(itlb_miss_handler)
@@ -1192,7 +1192,7 @@ i_pte_not_present:
EXCEPTION_LOAD_GPR4
EXCEPTION_LOAD_GPR5
EXCEPTION_LOAD_GPR6
- EXCEPTION_HANDLE(_itlb_miss_page_fault_handler)
+ EXCEPTION_HANDLE(_insn_page_fault_handler)

/* ==============================================[ boot tlb handlers ]=== */

diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
index e2bfafc..34c755e 100644
--- a/arch/openrisc/mm/fault.c
+++ b/arch/openrisc/mm/fault.c
@@ -23,9 +23,15 @@
#include <asm/uaccess.h>
#include <asm/siginfo.h>
#include <asm/signal.h>
+#include <asm/spr_defs.h>

-#define NUM_TLB_ENTRIES 64
-#define TLB_OFFSET(add) (((add) >> PAGE_SHIFT) & (NUM_TLB_ENTRIES-1))
+#define NUM_DTLB_SETS (1 << ((mfspr(SPR_IMMUCFGR) & SPR_IMMUCFGR_NTS) >> \
+ SPR_DMMUCFGR_NTS_OFF))
+#define NUM_ITLB_SETS (1 << ((mfspr(SPR_IMMUCFGR) & SPR_IMMUCFGR_NTS) >> \
+ SPR_IMMUCFGR_NTS_OFF))
+
+#define NUM_DTLB_WAYS (1 + (mfspr(SPR_DMMUCFGR) & SPR_DMMUCFGR_NTW))
+#define NUM_ITLB_WAYS (1 + (mfspr(SPR_IMMUCFGR) & SPR_IMMUCFGR_NTW))

unsigned long pte_misses; /* updated by do_page_fault() */
unsigned long pte_errors; /* updated by do_page_fault() */
@@ -38,6 +44,31 @@ volatile pgd_t *current_pgd;
extern void die(char *, struct pt_regs *, long);

/*
+ * Peeks into the tlbs associated with 'address'.
+ * Return 1 on miss and 0 on hit.
+ */
+static int tlb_miss(ulong address, ulong vector)
+{
+ int i;
+ ulong mr;
+ ulong vpn = address >> PAGE_SHIFT;
+ ulong num_tlb_ways = (vector == 0x300) ? NUM_DTLB_WAYS : NUM_ITLB_WAYS;
+ ulong num_tlb_sets = (vector == 0x300) ? NUM_DTLB_SETS : NUM_ITLB_SETS;
+ ulong offset = vpn & num_tlb_sets;
+
+ for (i = 0; i < num_tlb_ways; i++) {
+ mr = (vector == 0x300) ?
+ mfspr_off(SPR_DTLBMR_BASE(0), offset + i*256) :
+ mfspr_off(SPR_ITLBMR_BASE(0), offset + i*256);
+
+ if (vpn == mr >> PAGE_SHIFT)
+ return 0;
+ }
+
+ return 1;
+}
+
+/*
* This routine handles page faults. It determines the address,
* and the problem, and then passes it off to one of the appropriate
* routines.
@@ -75,11 +106,12 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
*
* This verifies that the fault happens in kernel space
* and that the fault was not a protection error.
+ * TLB misses are always handled before protection errors,
+ * so protection errors can only happen on TLB hits.
*/

- if (address >= VMALLOC_START &&
- (vector != 0x300 && vector != 0x400) &&
- !user_mode(regs))
+ if (address >= VMALLOC_START && !user_mode(regs) &&
+ tlb_miss(address, vector))
goto vmalloc_fault;

/* If exceptions were enabled, we can reenable them here */

--
1.8.1.2