On Tue, Dec 15, 2020 at 08:56:41PM +0000, Lorenzo Stoakes wrote: > pgt_buf is used to allocate page tables on initial direct page mapping > bootstrapping us into being able to allocate these before the direct > mapping makes further pages available. > > INIT_PGD_PAGE_COUNT is set to 6 pages (doubled for KASLR) - 3 (PUD, PMD, > PTE) for the 1 MiB ISA mapping and 3 more for the first direct mapping > assignment in each case providing 2 MiB of address space. > > This has not been updated for 5-level page tables which additionally has a > P4D page table level above PUD. > > In most instances this will not have a material impact as the first 4 page > levels allocated for the ISA mapping will provide sufficient address space > to encompass all further address mappings. If the first direct mapping is > within 512 GiB of the ISA mapping we need only add a PMD and PTE in the > instance where we are using 4 KiB page tables (e.g. CONFIG_DEBUG_PAGEALLOC > is enabled) and only a PMD if we can use 2 MiB pages (the first allocation > is limited to PMD_SIZE so we can't use a GiB page there). > > However if we have more than 512 GiB of RAM and are allocating 4 KiB page > size we require 3 further page tables and if we have more than 256 TiB of > RAM at 4 KiB or 2 MiB page size we require a further 3 or 4 page tables > respectively. > > This patch updates INIT_PGD_PAGE_COUNT to reflect this. > > Signed-off-by: Lorenzo Stoakes <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]> -- Kirill A. Shutemov
