Messages in this thread |  | | Date | Tue, 4 Sep 2018 11:13:14 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH 2/2] x86/mm/KASLR: Adjust the vmemmap size according to paging mode |
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On Mon, Sep 03, 2018 at 10:52:13PM +0800, Baoquan He wrote: > On 09/03/18 at 01:26pm, Kirill A. Shutemov wrote: > > On Mon, Sep 03, 2018 at 03:47:18PM +0800, Baoquan He wrote: > > > On 09/02/18 at 11:52pm, Kirill A. Shutemov wrote: > > > > On Thu, Aug 30, 2018 at 11:25:12PM +0800, Baoquan He wrote: > > > > > Hi Kirill, > > > > > > > > > > I made a new version according to your suggestion, just a little > > > > > different, I didn't make 1TB as default, just calculate with the actual > > > > > size, then align up to 1TB boundary. Just found kcore is printing more > > > > > entries than before, I thought it's caused by my code, later got it was > > > > > touchde by other people. > > > > > > > > > > Any comment about this? I can change accordingly. > > > > > > > > Looks good to me. > > > > > > > > But there's corner case when struct page is unreasonably large and > > > > vmemmap_size will be way to large. We probably have to report an error if > > > > we cannot fit vmemmap properly into virtual memory layout. > > > > > > Hmm, sizeof(struct page) can't exceed one whole page surely, otherwise > > > system bootup can't go over vmemmap initlization. Except of this, we may > > > need think about the virtual memory layout which vmemmap can be allowed > > > to occupy. > > > > > > If KASAN enabled, KASLR disabled, > > > 4-level 1TB + 1TB hole (2TB) > > > 5-level 512TB + 2034TB hole (2.5PB) > > > > > > If KASAN disabled, KASLR enabled, > > > 4-level 1TB + 1TB hole + 16TB (18TB) > > > 5-level 512TB + 2034TB hole + 8PB (10.5PB) > > > > > > So, as you can see, if add check in memory KASLR code, we should only > > > consider KASLR enabled case. We possibly don't need to worry about > > > 5-level case since the size 10.5PB is even bigger than the maximum > > > physical RAM mapping size. For 4-level, 18TB align to multiples of 2, it > > > will be 32 times of the current 1TB, then we usually assume 64 as the > > > default value of sizeof(struct page), then 64*32 == 1024. So we can add > > > check like this, what do you think? Or any other idea? > > > > Looks reasonable to me. > > > > But I would have the BUILD_BUG_ON() in generic code. If you struct page is > > more than 1/4 of PAGE_SIZE something is horribly broken. > > Just the 1/4 of PAGE_SIZE is based on analysis of KASLR case. If > non-KASLR case, it may not be that value.
Even if it technically possible to have struct page larger than PAGE_SIZE/4, it's just insane.
> Not sure if it's OK to put it in generic code, and haven't thought of a > good place, maybe in setup_arch(), just at the beginning?
I don't see an obvious place too. Maybe free_area_init_nodes()?
-- Kirill A. Shutemov
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