Re: [PATCH 4/6] MIPS: tlbex: Fix bugs in tlbchange handler

[David Daney <ddaney.cavm@gmail.com>]

On 01/26/2016 05:26 AM, Huacai Chen wrote:
> If a tlb miss triggered when EXL=1,

How is that possible?  The exception handlers are not in mapped memory, 
and we clear EXL very early in the exception handlers.

In valid code, how are you getting TLB related exceptions when EXL=1?

> tlb refill exception is treated as
> tlb invalid exception, so tlbp may fails. In this situation, CP0_Index
> register doesn't contain a valid value. This may not be a problem for
> VTLB since it is fully-associative. However, FTLB is set-associative so
> not every tlb entry is valid for a specific address. Thus, we should
> use tlbwr instead of tlbwi when tlbp fails.
>
> There is a similar case for huge page, so build_huge_tlb_write_entry()
> is also modified. If wmode != tlb_random, that means the caller is tlb
> invalid handler, we should select tlbr/tlbi depend on the tlbp result.
>
> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> ---
>   arch/mips/mm/tlbex.c | 31 ++++++++++++++++++++++++++++++-
>   1 file changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
> index d0975cd..da68ffb 100644
> --- a/arch/mips/mm/tlbex.c
> +++ b/arch/mips/mm/tlbex.c
> @@ -173,7 +173,10 @@ enum label_id {
>   	label_large_segbits_fault,
>   #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
>   	label_tlb_huge_update,
> +	label_tail_huge_miss,
> +	label_tail_huge_done,
>   #endif
> +	label_tail_miss,
>   };
>
>   UASM_L_LA(_second_part)
> @@ -192,7 +195,10 @@ UASM_L_LA(_r3000_write_probe_fail)
>   UASM_L_LA(_large_segbits_fault)
>   #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
>   UASM_L_LA(_tlb_huge_update)
> +UASM_L_LA(_tail_huge_miss)
> +UASM_L_LA(_tail_huge_done)
>   #endif
> +UASM_L_LA(_tail_miss)
>
>   static int hazard_instance;
>
> @@ -706,8 +712,24 @@ static void build_huge_tlb_write_entry(u32 **p, struct uasm_label **l,
>   	uasm_i_ori(p, tmp, tmp, PM_HUGE_MASK & 0xffff);
>   	uasm_i_mtc0(p, tmp, C0_PAGEMASK);
>
> -	build_tlb_write_entry(p, l, r, wmode);
> +	if (wmode == tlb_random) { /* Caller is TLB Refill Handler */
> +		build_tlb_write_entry(p, l, r, wmode);
> +		build_restore_pagemask(p, r, tmp, label_leave, restore_scratch);
> +		return;
> +	}
> +
> +	/* Caller is TLB Load/Store/Modify Handler */
> +	uasm_i_mfc0(p, tmp, C0_INDEX);
> +	uasm_il_bltz(p, r, tmp, label_tail_huge_miss);
> +	uasm_i_nop(p);
> +	build_tlb_write_entry(p, l, r, tlb_indexed);
> +	uasm_il_b(p, r, label_tail_huge_done);
> +	uasm_i_nop(p);
> +
> +	uasm_l_tail_huge_miss(l, *p);
> +	build_tlb_write_entry(p, l, r, tlb_random);
>
> +	uasm_l_tail_huge_done(l, *p);
>   	build_restore_pagemask(p, r, tmp, label_leave, restore_scratch);
>   }
>
> @@ -2026,7 +2048,14 @@ build_r4000_tlbchange_handler_tail(u32 **p, struct uasm_label **l,
>   	uasm_i_ori(p, ptr, ptr, sizeof(pte_t));
>   	uasm_i_xori(p, ptr, ptr, sizeof(pte_t));
>   	build_update_entries(p, tmp, ptr);
> +	uasm_i_mfc0(p, ptr, C0_INDEX);
> +	uasm_il_bltz(p, r, ptr, label_tail_miss);
> +	uasm_i_nop(p);
>   	build_tlb_write_entry(p, l, r, tlb_indexed);
> +	uasm_il_b(p, r, label_leave);
> +	uasm_i_nop(p);
> +	uasm_l_tail_miss(l, *p);
> +	build_tlb_write_entry(p, l, r, tlb_random);
>   	uasm_l_leave(l, *p);
>   	build_restore_work_registers(p);
>   	uasm_i_eret(p); /* return from trap */
>