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Subject[PATCH 3.16 77/87] MIPS: Add missing EHB in mtc0 -> mfc0 sequence.
3.16.75-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Dmitry Korotin <dkorotin@wavecomp.com>

commit 0b24cae4d535045f4c9e177aa228d4e97bad212c upstream.

Add a missing EHB (Execution Hazard Barrier) in mtc0 -> mfc0 sequence.
Without this execution hazard barrier it's possible for the value read
back from the KScratch register to be the value from before the mtc0.

Reproducible on P5600 & P6600.

The hazard is documented in the MIPS Architecture Reference Manual Vol.
III: MIPS32/microMIPS32 Privileged Resource Architecture (MD00088), rev
6.03 table 8.1 which includes:

Producer | Consumer | Hazard
----------|----------|----------------------------
mtc0 | mfc0 | any coprocessor 0 register

Signed-off-by: Dmitry Korotin <dkorotin@wavecomp.com>
[paul.burton@mips.com:
- Commit message tweaks.
- Add Fixes tags.
- Mark for stable back to v3.15 where P5600 support was introduced.]
Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: 3d8bfdd03072 ("MIPS: Use C0_KScratch (if present) to hold PGD pointer.")
Fixes: 829dcc0a956a ("MIPS: Add MIPS P5600 probe support")
Cc: linux-mips@vger.kernel.org
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/mips/mm/tlbex.c | 29 ++++++++++++++++++++---------
1 file changed, 20 insertions(+), 9 deletions(-)

--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -374,6 +374,7 @@ static struct work_registers build_get_w
static void build_restore_work_registers(u32 **p)
{
if (scratch_reg >= 0) {
+ uasm_i_ehb(p);
UASM_i_MFC0(p, 1, c0_kscratch(), scratch_reg);
return;
}
@@ -665,10 +666,12 @@ static void build_restore_pagemask(u32 *
uasm_i_mtc0(p, 0, C0_PAGEMASK);
uasm_il_b(p, r, lid);
}
- if (scratch_reg >= 0)
+ if (scratch_reg >= 0) {
+ uasm_i_ehb(p);
UASM_i_MFC0(p, 1, c0_kscratch(), scratch_reg);
- else
+ } else {
UASM_i_LW(p, 1, scratchpad_offset(0), 0);
+ }
} else {
/* Reset default page size */
if (PM_DEFAULT_MASK >> 16) {
@@ -906,10 +909,12 @@ build_get_pgd_vmalloc64(u32 **p, struct
uasm_i_jr(p, ptr);

if (mode == refill_scratch) {
- if (scratch_reg >= 0)
+ if (scratch_reg >= 0) {
+ uasm_i_ehb(p);
UASM_i_MFC0(p, 1, c0_kscratch(), scratch_reg);
- else
+ } else {
UASM_i_LW(p, 1, scratchpad_offset(0), 0);
+ }
} else {
uasm_i_nop(p);
}
@@ -1215,6 +1220,7 @@ build_fast_tlb_refill_handler (u32 **p,
UASM_i_MTC0(p, odd, C0_ENTRYLO1); /* load it */

if (c0_scratch_reg >= 0) {
+ uasm_i_ehb(p);
UASM_i_MFC0(p, scratch, c0_kscratch(), c0_scratch_reg);
build_tlb_write_entry(p, l, r, tlb_random);
uasm_l_leave(l, *p);
@@ -1466,12 +1472,14 @@ static void build_setup_pgd(void)
uasm_i_dinsm(&p, a0, 0, 29, 64 - 29);
uasm_l_tlbl_goaround1(&l, p);
UASM_i_SLL(&p, a0, a0, 11);
- uasm_i_jr(&p, 31);
UASM_i_MTC0(&p, a0, C0_CONTEXT);
+ uasm_i_jr(&p, 31);
+ uasm_i_ehb(&p);
} else {
/* PGD in c0_KScratch */
- uasm_i_jr(&p, 31);
UASM_i_MTC0(&p, a0, c0_kscratch(), pgd_reg);
+ uasm_i_jr(&p, 31);
+ uasm_i_ehb(&p);
}
#else
#ifdef CONFIG_SMP
@@ -1485,13 +1493,16 @@ static void build_setup_pgd(void)
UASM_i_LA_mostly(&p, a2, pgdc);
UASM_i_SW(&p, a0, uasm_rel_lo(pgdc), a2);
#endif /* SMP */
- uasm_i_jr(&p, 31);

/* if pgd_reg is allocated, save PGD also to scratch register */
- if (pgd_reg != -1)
+ if (pgd_reg != -1) {
UASM_i_MTC0(&p, a0, c0_kscratch(), pgd_reg);
- else
+ uasm_i_jr(&p, 31);
+ uasm_i_ehb(&p);
+ } else {
+ uasm_i_jr(&p, 31);
uasm_i_nop(&p);
+ }
#endif
if (p >= tlbmiss_handler_setup_pgd_end)
panic("tlbmiss_handler_setup_pgd space exceeded");
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