On 4/9/25 4:25 PM, Alexander Gordeev wrote:
> On Wed, Apr 09, 2025 at 04:10:58PM +0200, Andrey Ryabinin wrote:
>
> Hi Andrey,
>
>>> @@ -301,7 +301,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep,
>>> unsigned long addr,
>>> if (likely(!pte_none(ptep_get(ptep))))
>>> return 0;
>>>
>>> - page = __get_free_page(GFP_KERNEL);
>>> + page = __get_free_page(GFP_ATOMIC);
>>> if (!page)
>>> return -ENOMEM;
>>>
>>
>> I think a better way to fix this would be moving out allocation from atomic
>> context. Allocate page prior
>> to apply_to_page_range() call and pass it down to
>> kasan_populate_vmalloc_pte().
>
> I think the page address could be passed as the parameter to
> kasan_populate_vmalloc_pte().
We'll need to pass it as 'struct page **page' or maybe as pointer to some
struct, e.g.:
struct page_data {
struct page *page;
};
So, the kasan_populate_vmalloc_pte() would do something like this:
kasan_populate_vmalloc_pte() {
if (!pte_none)
return 0;
if (!page_data->page)
return -EAGAIN;
//use page to set pte
//NULLify pointer so that next kasan_populate_vmalloc_pte() will bail
// out to allocate new page
page_data->page = NULL;
}
And it might be good idea to add 'last_addr' to page_data, so that we know
where we stopped
so that the next apply_to_page_range() call could continue, instead of starting
from the beginning.
>
>> Whenever kasan_populate_vmalloc_pte() will require additional page we could
>> bail out with -EAGAIN,
>> and allocate another one.
>
> When would it be needed? kasan_populate_vmalloc_pte() handles just one page.
>
apply_to_page_range() goes over range of addresses and calls
kasan_populate_vmalloc_pte()
multiple times (each time with different 'addr' but the same '*unused' arg).
Things will go wrong
if you'll use same page multiple times for different addresses.
> Thanks!
