On 16.04.2025 12:44, Oleksii Kurochko wrote: > > On 4/15/25 12:07 PM, Jan Beulich wrote: >> On 14.04.2025 17:56, Oleksii Kurochko wrote: >>> --- a/xen/arch/riscv/mm.c >>> +++ b/xen/arch/riscv/mm.c >>> @@ -31,20 +31,30 @@ unsigned long __ro_after_init phys_offset; /* = >>> load_start - XEN_VIRT_START */ >>> #define LOAD_TO_LINK(addr) ((unsigned long)(addr) - phys_offset) >>> >>> /* >>> - * It is expected that Xen won't be more then 2 MB. >>> + * It is expected that Xen won't be more then XEN_VIRT_SIZE. >>> * The check in xen.lds.S guarantees that. >>> - * At least 3 page tables (in case of Sv39 ) are needed to cover 2 MB. >>> - * One for each page level table with PAGE_SIZE = 4 Kb. >>> * >>> - * One L0 page table can cover 2 MB(512 entries of one page table * >>> PAGE_SIZE). >>> + * Root page table is shared with the initial mapping and is declared >>> + * separately. (look at stage1_pgtbl_root) >>> * >>> - * It might be needed one more page table in case when Xen load address >>> - * isn't 2 MB aligned. >>> + * An amount of page tables between root page table and L0 page table >>> + * (in the case of Sv39 it covers L1 table): >>> + * (CONFIG_PAGING_LEVELS - 2) are needed for an identity mapping and >>> + * the same amount are needed for Xen. >>> * >>> - * CONFIG_PAGING_LEVELS page tables are needed for the identity mapping, >>> - * except that the root page table is shared with the initial mapping >>> + * An amount of L0 page tables: >>> + * (512 entries of one L0 page table covers 2MB == >>> 1<<XEN_PT_LEVEL_SHIFT(1)) >>> + * XEN_VIRT_SIZE >> XEN_PT_LEVEL_SHIFT(1) are needed for Xen and >>> + * one L0 is needed for identity mapping. >>> */ >>> -#define PGTBL_INITIAL_COUNT ((CONFIG_PAGING_LEVELS - 1) * 2 + 1) >>> +#define PGTBL_INITIAL_COUNT ((CONFIG_PAGING_LEVELS - 2) * 2 + \ >>> + (XEN_VIRT_SIZE >> XEN_PT_LEVEL_SHIFT(1)) + 1) >> I'm still struggling here. In the original expression, the +1 was to cover >> the root page table, wasn't it? > > |+1| was added to cover the case where the Xen address is not 2MB-aligned.
Oh, okay. > For the root page table, we use a separate variable|stage1_pgtbl_root|. > Since the root page table is shared with the identity mapping, it is not > included in|PGTBL_INITIAL_COUNT|. Makes all sense then, thanks. Jan
