Re: [PATCH v10 4/5] x86/kasan: support KASAN_VMALLOC

Daniel Axtens
2019-10-30T13:50:13Z

Andrey Ryabinin <aryabinin@virtuozzo.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@google.com>
>> Signed-off-by: Daniel Axtens <dja@axtens.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@virtuozzo.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