On Fri, Jun 21, 2019 at 11:12 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Fri 21-06-19 10:57:35, Alexander Potapenko wrote: > > On Fri, Jun 21, 2019 at 9:09 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > [...] > > > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > > > > index fd5c95ff9251..2f75dd0d0d81 100644 > > > > --- a/kernel/kexec_core.c > > > > +++ b/kernel/kexec_core.c > > > > @@ -315,7 +315,7 @@ static struct page *kimage_alloc_pages(gfp_t gfp_mask, unsigned int order) > > > > arch_kexec_post_alloc_pages(page_address(pages), count, > > > > gfp_mask); > > > > > > > > - if (gfp_mask & __GFP_ZERO) > > > > + if (want_init_on_alloc(gfp_mask)) > > > > for (i = 0; i < count; i++) > > > > clear_highpage(pages + i); > > > > } > > > > > > I am not really sure I follow here. Why do we want to handle > > > want_init_on_alloc here? The allocated memory comes from the page > > > allocator and so it will get zeroed there. arch_kexec_post_alloc_pages > > > might touch the content there but is there any actual risk of any kind > > > of leak? > > You're right, we don't want to initialize this memory if init_on_alloc is on. > > We need something along the lines of: > > if (!static_branch_unlikely(&init_on_alloc)) > > if (gfp_mask & __GFP_ZERO) > > // clear the pages > > > > Another option would be to disable initialization in alloc_pages() using a flag. > > Or we can simply not care and keen the code the way it is. First of all > it seems that nobody actually does use __GFP_ZERO unless I have missed > soemthing > - kimage_alloc_pages(KEXEC_CONTROL_MEMORY_GFP, order); # GFP_KERNEL | __GFP_NORETRY > - kimage_alloc_pages(gfp_mask, 0); > - kimage_alloc_page(image, GFP_KERNEL, KIMAGE_NO_DEST); > - kimage_alloc_page(image, GFP_HIGHUSER, maddr); > > but even if we actually had a user do we care about double intialization > for something kexec related? It is not any hot path AFAIR. Yes, sounds good. Spraying the code with too many checks for init_on_alloc doesn't really look nice. > -- > Michal Hocko > SUSE Labs -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
