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Subject: Re: [PATCH v11 6/6] powerpc: Book3S 64-bit outline-only KASAN support
To:     Daniel Axtens <dja@axtens.net>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
        kasan-dev@googlegroups.com, aneesh.kumar@linux.ibm.com,
        bsingharora@gmail.com
References: <20210319144058.772525-1-dja@axtens.net>
 <20210319144058.772525-7-dja@axtens.net>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <fc849719-e2c0-bbcb-c58e-f4ff3e9c5f18@csgroup.eu>
Date:   Wed, 21 Apr 2021 14:29:38 +0200
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Le 19/03/2021 à 15:40, Daniel Axtens a écrit :
> diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
> index aca354fb670b..63672aa656e8 100644
> --- a/arch/powerpc/mm/ptdump/ptdump.c
> +++ b/arch/powerpc/mm/ptdump/ptdump.c
> @@ -20,6 +20,7 @@
>   #include <linux/seq_file.h>
>   #include <asm/fixmap.h>
>   #include <linux/const.h>
> +#include <linux/kasan.h>
>   #include <asm/page.h>
>   #include <asm/hugetlb.h>
>   
> @@ -317,6 +318,23 @@ static void walk_pud(struct pg_state *st, p4d_t *p4d, unsigned long start)
>   	unsigned long addr;
>   	unsigned int i;
>   
> +#if defined(CONFIG_KASAN) && defined(CONFIG_PPC_BOOK3S_64)
> +	/*
> +	 * On radix + KASAN, we want to check for the KASAN "early" shadow
> +	 * which covers huge quantities of memory with the same set of
> +	 * read-only PTEs. If it is, we want to note the first page (to see
> +	 * the status change), and then note the last page. This gives us good
> +	 * results without spending ages noting the exact same PTEs over 100s of
> +	 * terabytes of memory.
> +	 */
> +	if (p4d_page(*p4d) == virt_to_page(lm_alias(kasan_early_shadow_pud))) {
> +		walk_pmd(st, pud, start);
> +		addr = start + (PTRS_PER_PUD - 1) * PUD_SIZE;
> +		walk_pmd(st, pud, addr);
> +		return;
> +	}
> +#endif
> +
>   	for (i = 0; i < PTRS_PER_PUD; i++, pud++) {
>   		addr = start + i * PUD_SIZE;
>   		if (!pud_none(*pud) && !pud_is_leaf(*pud))


The above changes should not be necessary once PPC_PTDUMP is converted to GENERIC_PTDUMP.

See https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=239795


Christophe