Re: [PATCH-for-9.1] target/mips: Fix execution mode in page_table_walk_refill()

[Richard Henderson]

On 8/12/24 02:54, Philippe Mathieu-Daudé wrote:
> When refactoring page_table_walk_refill() in commit 4e999bf419
> we replaced the execution mode and forced it to kernel mode.
> Restore the previous behavior to also get supervisor / user modes.
>
> Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
> Reported-by: Waldemar Brodkorb <wbx@uclibc-ng.org>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2470
> Fixes: 4e999bf419 ("target/mips: Pass ptw_mmu_idx down from mips_cpu_tlb_fill")
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   target/mips/tcg/sysemu/tlb_helper.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/target/mips/tcg/sysemu/tlb_helper.c 
> b/target/mips/tcg/sysemu/tlb_helper.c
> index 3ba6d369a6..e7ae4f0bef 100644
> --- a/target/mips/tcg/sysemu/tlb_helper.c
> +++ b/target/mips/tcg/sysemu/tlb_helper.c
> @@ -940,8 +940,9 @@ bool mips_cpu_tlb_fill(CPUState *cs, vaddr address, int 
> size,
>            * Memory reads during hardware page table walking are performed
>            * as if they were kernel-mode load instructions.
>            */
> -        int ptw_mmu_idx = (env->hflags & MIPS_HFLAG_ERL ?
> -                           MMU_ERL_IDX : MMU_KERNEL_IDX);
> +        int ptw_mmu_idx = (env->hflags & MIPS_HFLAG_ERL)
> +                          ? MMU_ERL_IDX
> +                          : (env->hflags & MIPS_HFLAG_KSU);

This contradicts the comment above.
If this code change is correct, then the comment isn't.

But the comment certainly makes sense -- page tables are never accessible to 
user mode.


r~