linux-kernel - Re: [PATCH v10 4/5] x86/kasan: support KASAN

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Date:   Tue, 29 Oct 2019 20:21:03 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Daniel Axtens <dja@...ens.net>, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, x86@...nel.org, glider@...gle.com,
        luto@...nel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, dvyukov@...gle.com, christophe.leroy@....fr
Cc:     linuxppc-dev@...ts.ozlabs.org, gor@...ux.ibm.com,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v10 4/5] x86/kasan: support KASAN_VMALLOC



On 10/29/19 7:20 AM, Daniel Axtens wrote:
> In the case where KASAN directly allocates memory to back vmalloc
> space, don't map the early shadow page over it.
> 
> We prepopulate pgds/p4ds for the range that would otherwise be empty.
> This is required to get it synced to hardware on boot, allowing the
> lower levels of the page tables to be filled dynamically.
> 
> Acked-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Daniel Axtens <dja@...ens.net>
> 
> ---

> +static void __init kasan_shallow_populate_pgds(void *start, void *end)
> +{
> +	unsigned long addr, next;
> +	pgd_t *pgd;
> +	void *p;
> +	int nid = early_pfn_to_nid((unsigned long)start);

This doesn't make sense. start is not even a pfn. With linear mapping 
we try to identify nid to have the shadow on the same node as memory. But 
in this case we don't have memory or the corresponding shadow (yet),
we only install pgd/p4d.
I guess we could just use NUMA_NO_NODE.

The rest looks ok, so with that fixed:

Reviewed-by: Andrey Ryabinin <aryabinin@...tuozzo.com>