Unverified Commit 0b24cae4 authored by Dmitry Korotin's avatar Dmitry Korotin Committed by Paul Burton
Browse files

MIPS: Add missing EHB in mtc0 -> mfc0 sequence. 



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: default avatarDmitry 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: default avatarPaul Burton <paul.burton@mips.com>
Fixes: 3d8bfdd0 ("MIPS: Use C0_KScratch (if present) to hold PGD pointer.")
Fixes: 829dcc0a ("MIPS: Add MIPS P5600 probe support")
Cc: linux-mips@vger.kernel.org
Cc: stable@vger.kernel.org # v3.15+
parent 637dfa0f

arch/mips/mm/tlbex.c

+20 −9
Original line number Diff line number Diff line
@@ -391,6 +391,7 @@ static struct work_registers build_get_work_registers(u32 **p) 
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;

	}
@@ -668,10 +669,12 @@ static void build_restore_pagemask(u32 **p, struct uasm_reloc **r, 
			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) {
@@ -938,10 +941,12 @@ build_get_pgd_vmalloc64(u32 **p, struct uasm_label **l, struct uasm_reloc **r, 
		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);

		}
@@ -1258,6 +1263,7 @@ build_fast_tlb_refill_handler (u32 **p, struct uasm_label **l, 
	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);
@@ -1603,15 +1609,17 @@ 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);

		if (cpu_has_ldpte)

			UASM_i_MTC0(&p, a0, C0_PWBASE);

		else

			UASM_i_MTC0(&p, a0, c0_kscratch(), pgd_reg);

		uasm_i_jr(&p, 31);

		uasm_i_ehb(&p);

	}

#else

#ifdef CONFIG_SMP
@@ -1625,13 +1633,16 @@ 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 >= (u32 *)tlbmiss_handler_setup_pgd_end)

		panic("tlbmiss_handler_setup_pgd space exceeded");

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