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. 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? > > > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c > > index 1db8e166455e..776ec759a87c 100644 > > --- a/arch/x86/mm/kaslr.c > > +++ b/arch/x86/mm/kaslr.c > > @@ -90,6 +90,7 @@ void __init kernel_randomize_memory(void) > > BUILD_BUG_ON(vaddr_start >= vaddr_end); > > BUILD_BUG_ON(vaddr_end != CPU_ENTRY_AREA_BASE); > > BUILD_BUG_ON(vaddr_end > __START_KERNEL_map); > > + BUILD_BUG_ON(sizeof(struct page ) > PAGE_SIZE/4); > > Nitpick: redundant space before ')'. > > > > > if (!kaslr_memory_enabled()) > > return; > > > > > > For 5-level paging mode, we > > may not need to worry about that. Since KASAN > > > > ***4-level*** > > ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB) > > ... unused hole ... > > ffffec0000000000 - fffffbffffffffff (=44 bits) kasan shadow memory (16TB) > > ... unused hole ... > > > > > > > > ***5-level*** > > ffd4000000000000 - ffd5ffffffffffff (=49 bits) virtual memory map (512TB) > > ... unused hole ... > > ffdf000000000000 - fffffc0000000000 (=53 bits) kasan shadow memory (8PB) > > > > > > > > -- > > > Kirill A. Shutemov > > -- > Kirill A. Shutemov