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!