On 07/31/2014 04:54 AM, James Hogan wrote:
Hi,
On 31/07/14 02:13, David Daney wrote:
On 07/30/2014 05:48 PM, Huacai Chen wrote:
For non-Octeon CPU, htlb_info.huge_pte is equal to K0, but I don't
know much about Octeon. So I think you know whether we should use K0
or htlb_info.huge_pte here, since you are the original author.
This is why I requested that somebody show me a disassembly of the
faulty handler. I cannot tell where the problem is unless I see that.
Really I think the problem is in build_is_huge_pte(), where we are
clobbering 'tmp' which is K0.
So you could reload tmp/K0 in build_is_huge_pte().
Here's the difference with this patch (using k0) on an Octeon I have to
hand, with some slightly munged offsets for nicer diffing:
#define _PAGE_PRESENT_SHIFT 0
#define _PAGE_READ_SHIFT 0
#define _PAGE_WRITE_SHIFT 1
#define _PAGE_ACCESSED_SHIFT 2
#define _PAGE_MODIFIED_SHIFT 3
#define _PAGE_HUGE_SHIFT 4
#define _PAGE_SPLITTING_SHIFT 5
#define _PAGE_NO_EXEC_SHIFT 6
#define _PAGE_NO_READ_SHIFT 7
#define _PAGE_GLOBAL_SHIFT 8
#define _PAGE_VALID_SHIFT 9
#define _PAGE_DIRTY_SHIFT 10
#define _PFN_SHIFT 14
00000000 <r4000_tlb_refill>:
+ 0: df7a0000 ld k0,0(k1)
Completely redundant, it is not used and then clobbered...
4: 00210a3a dror at,at,0x8
8: 40a11000 dmtc0 at,c0_entrylo0
c: 64214000 daddiu at,at,16384
10: 40a11800 dmtc0 at,c0_entrylo1
14: 3c1a001f lui k0,0x1f
... here.
18: 375ae000 ori k0,k0,0xe000
1c: 409a2800 mtc0 k0,c0_pagemask
20: 000000c0 ehb
24: 42000006 tlbwr
28: 40802800 mtc0 zero,c0_pagemask
- 28: 1000002e b e4 <r4000_tlb_refill+0xe4>
+ 2c: 1000002d b e4 <r4000_tlb_refill+0xe4>
30: 4021f802 dmfc0 at,$31,2
- 30: 07400019 bltz k0,98 <r4000_tlb_refill+0x98>
+ 34: 07400018 bltz k0,98 <r4000_tlb_refill+0x98>
38: 3c1b81da lui k1,0x81da
3c: 3c1b8113 lui k1,0x8113
- 3c: 277b7ef0 addiu k1,k1,32496
+ 40: 277b7f00 addiu k1,k1,32512
44: 03600008 jr k1
48: 4021f802 dmfc0 at,$31,2
...
80: 403a4000 dmfc0 k0,c0_badvaddr
84: 403bf803 dmfc0 k1,$31,3
88: 40a1f802 dmtc0 at,$31,2
8c: 001a0a3e dsrl32 at,k0,0x8
- 90: 1420ffe7 bnez at,30 <r4000_tlb_refill+0x30>
+ 90: 1420ffe8 bnez at,34 <r4000_tlb_refill+0x34>
94: 001a0efa dsrl at,k0,0x1b
98: 30211ff8 andi at,at,0x1ff8
9c: 7c3bda0a ldx k1,k1(at)
a0: 001a0cba dsrl at,k0,0x12
a4: 30210ff8 andi at,at,0xff8
a8: 403aa000 dmfc0 k0,c0_xcontext
ac: 7c3b0a0a ldx at,k1(at)
b0: 335a0ff0 andi k0,k0,0xff0
b4: e824ffd2 bbit1 at,0x4,0 <r4000_tlb_refill>
b8: 00000000 nop
bc: 7c3ada0a ldx k1,k0(at)
c0: 675a0008 daddiu k0,k0,8
c4: 7c3ad20a ldx k0,k0(at)
c8: 003bda3a dror k1,k1,0x8
cc: 40bb1000 dmtc0 k1,c0_entrylo0
d0: 003ad23a dror k0,k0,0x8
d4: 40ba1800 dmtc0 k0,c0_entrylo1
d8: 4021f802 dmfc0 at,$31,2
dc: 000000c0 ehb
e0: 42000006 tlbwr
e4: 42000018 eret
b4 is apparently where it branches back to the huge page case at the
beginning. In that case the at register (htlb_info.huge_pte) is set to
*(k1+at) instead of *(k1), so loading to htlb_info.huge_pte instead of
k0 would I think be bad and change the behaviour. So forget my suggestion!
On the other hand loading the pte to k0 is redundant when
build_fast_tlb_refill_handler is used (which depends on bbit1), and also
in the other case if bbit1 is available since it won't get clobbered by
build_is_huge_pte().
Maybe the reload should simply be conditional on !use_bbit_insns()?
That was kind of my suggestion. What happens if you do something like
(untested):
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -716,6 +716,7 @@ build_is_huge_pte(u32 **p, struct uasm_reloc **r,
unsigned int tmp,
} else {
uasm_i_andi(p, tmp, tmp, _PAGE_HUGE);
uasm_il_bnez(p, r, tmp, lid);
+ UASM_i_LW(p, tmp, 0, pmd);
}
}
or
diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index f99ec587..341add1 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -1299,6 +1299,8 @@ static void build_r4000_tlb_refill_handler(void)
}
#ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
uasm_l_tlb_huge_update(&l, p);
+ if (!use_bbit_insns())
+ UASM_i_LW(&p, K0, 0, K1);
build_huge_update_entries(&p, htlb_info.huge_pte, K1);
build_huge_tlb_write_entry(&p, &l, &r, K0, tlb_random,
htlb_info.restore_scratch);
Cheers
James
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