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

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Message-ID: <87sgnamjg2.fsf@dja-thinkpad.axtens.net>
Date:   Thu, 31 Oct 2019 00:50:05 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        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

Andrey Ryabinin <aryabinin@...tuozzo.com> writes:

> 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.

Ah wow, that's quite the clanger on my part.

There are a couple of other invocations of early_pfn_to_nid in that file
that use an address directly, but at least they reference actual memory.
I'll send a separate patch to fix those up.

> The rest looks ok, so with that fixed:
>
> Reviewed-by: Andrey Ryabinin <aryabinin@...tuozzo.com>

Thanks heaps! I've fixed up the nit you identifed in the first patch,
and I agree that the last patch probably isn't needed. I'll respin the
series shortly.

Regards,
Daniel