On 29.08.2025 15:32, Teddy Astie wrote: > Le 28/08/2025 à 14:30, Jan Beulich a écrit : >> On 21.08.2025 17:25, Teddy Astie wrote: >>> @@ -686,10 +691,31 @@ static int domain_construct_memmap(libxl__gc *gc, >>> /* We always own at least one lowmem entry. */ >>> unsigned int e820_entries = 1; >>> struct e820entry *e820 = NULL; >>> + uint64_t highmem_start = ((uint64_t)1 << 32); >>> uint64_t highmem_size = >>> dom->highmem_end ? dom->highmem_end - (1ull << 32) : >>> 0; >>> uint32_t lowmem_start = dom->device_model ? >>> GUEST_LOW_MEM_START_DEFAULT : 0; >>> unsigned page_size = XC_DOM_PAGE_SIZE(dom); >>> + /* Special region starts at the first 1G boundary after the highmem */ >>> + uint64_t special_region_start = >>> + (highmem_start + highmem_size + GB(1) - 1) & ~(GB(1) - 1); >> >> That is, inaccessible before entering PAE mode? > > Yes, I expect this to be only used by newer guests which hopefully > aren't limited to 4G range (i.e supports PAE or long mode). The issue of > trying to put that below 4G is that much of the space is already taken > for the MMIO hole, so that area would quite complicated with more > special regions.
Which excludes any boot loaders simple enough to not even require entering paging mode. >>> --- a/xen/include/public/arch-x86/hvm/start_info.h >>> +++ b/xen/include/public/arch-x86/hvm/start_info.h >>> @@ -99,6 +99,13 @@ >>> #define XEN_HVM_MEMMAP_TYPE_DISABLED 6 >>> #define XEN_HVM_MEMMAP_TYPE_PMEM 7 >>> >>> +/* Xen-specific types (OEM-specific range of the ACPI spec) */ >>> +#define XEN_HVM_MEMMAP_TYPE_SHARED_INFO 0xF0000001 /* Shared info page */ >>> +#define XEN_HVM_MEMMAP_TYPE_GRANT_TABLE 0xF0000002 /* Grant table pages >>> */ >>> +#define XEN_HVM_MEMMAP_TYPE_GNTTAB_STATUS 0xF0000003 /* Grant table status >>> page (v2) */ >>> +#define XEN_HVM_MEMMAP_TYPE_FOREIGN_REG 0xF0000004 /* Suitable region >>> for grant mappings */ >>> + /* and foreign >>> mappings */ >> >> I question it being legitimate for us to introduce new E820 types. > > These E820 types are (at least in ACPI specification) in the OEM-defined > range which seems appropriate for me to use for Xen-specific mappings. Just that we're not an OEM. Jan
