Re: [PATCH v4] Support madvise(MADV_DONTDUMP) when creating core dumps for qemu-user

[Richard Henderson <richard.henderson@linaro.org>]

On 5/6/25 11:34, Jon Wilson wrote:
> +    case MADV_DONTDUMP:
> +        if (len > 0) {
> +            /*
> +             * To set the page permissons, we must OR our new flags with the
> +             * existing flags. Only mark the pages as PAGE_DONTDUMP if the
> +             * entire range has the same flags. If any part of the range
> +             * differs, we would need to process it one page at a time which
> +             * might not be very performant. Since we are not obliged to respect
> +             * this flag, we will support it for the most likely usage scenario.
> +             * Note that we don't set PAGE_ANON, since this can only be set with
> +             * new mappings.
> +             */
> +            int flg = page_get_flags(start);
> +            if (page_check_range(start, len, flg)) {
> +                page_set_flags(start, start + len - 1, PAGE_DONTDUMP | (flg & ~PAGE_ANON) );
> +            }

There is an existing helper function, pageflags_set_clear, which could be promoted and 
exported to perform this OR.  Indeed, the bits-to-set and bits-to-clear interface would 
probably be clearer for all existing uses of page_set_flags, eliminating the need for the 
PAGE_RESET hack.

You don't want to clear PAGE_ANON.


r~