Re: [PATCH RFC 4/4] m68k equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY handling" If e.g. get_user() triggers a page fault and a fatal signal is caught, we might end up with handle_mm_fault() returning VM_FAULT_RETRY and not doing anything to page tables. In such case we must *not* return to the faulting insn - that would repeat the entire thing without making any progress; what we need instead is to treat that as failed (user) memory access.

[John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>]

Hi Michael,

On Mon, 2024-02-05 at 08:21 +1300, Michael Schmitz wrote:
> From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
>
> MSch: v4.4 backport compile errors fixes.
>
> Tested-by: Finn Thain <fthain@xxxxxxxxxxxxxx>
> Tested-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Michael Schmitz <schmitzmic@xxxxxxxxx>
> ---
>  arch/m68k/mm/fault.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
> index 6a94cdd0c830..f94df64c3784 100644
> --- a/arch/m68k/mm/fault.c
> +++ b/arch/m68k/mm/fault.c
> @@ -139,8 +139,11 @@ good_area:
>  	fault = handle_mm_fault(mm, vma, address, flags);
>  	pr_debug("handle_mm_fault returns %d\n", fault);
>  
> -	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
> +	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
> +		if (!user_mode(regs))
> +			goto no_context;
>  		return 0;
> +	}
>  
>  	if (unlikely(fault & VM_FAULT_ERROR)) {
>  		if (fault & VM_FAULT_OOM)

That subject looks like it contains the long description which should go
into the patch instead.

Adrian

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