3.16.75-rc1 review patch. If anyone has any objections, please let me know.
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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");