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kernel: mmu: install demand mappings for the on-demand linker sections

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This sets initial unpaged mappings for __ondemand_func code and
__ondemand_rodata variables. To achieve this, we have to augment the
backing store API.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2024-07-30 14:58:17 -04:00 • committed by Anas Nashif
commit 1e4fd23e58
4 changed files with 55 additions and 0 deletions
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1
Kconfig.zephyr
View file

@ -262,6 +262,7 @@ config LINKER_USE_PINNED_SECTION
config LINKER_USE_ONDEMAND_SECTION
bool "Use Evictable Linker Section"
depends on DEMAND_MAPPING
depends on !LINKER_USE_PINNED_SECTION
depends on !ARCH_MAPS_ALL_RAM
help

5
doc/kernel/memory_management/demand_paging.rst
View file

@ -179,6 +179,11 @@ which must be implemented:
free a backing store location (the ``location`` token) which can
then be used for subsequent page out operation.
* :c:func:`k_mem_paging_backing_store_location_query()` is called to obtain
the ``location`` token corresponding to storage content to be virtually
mapped and paged-in on demand. Most useful with
:kconfig:option:`CONFIG_DEMAND_MAPPING`.
* :c:func:`k_mem_paging_backing_store_page_in()` copies a data page
from the backing store location associated with the provided
``location`` token to the page pointed by ``K_MEM_SCRATCH_PAGE``.

16
include/zephyr/kernel/mm/demand_paging.h
View file

@ -349,6 +349,22 @@ int k_mem_paging_backing_store_location_get(struct k_mem_page_frame *pf,
*/
void k_mem_paging_backing_store_location_free(uintptr_t location);
/**
* Obtain persistent location token for on-demand content
*
* Unlike k_mem_paging_backing_store_location_get() this does not allocate
* any backing store space. Instead, it returns a location token corresponding
* to some fixed storage content to be paged in on demand. This is expected
* to be used in conjonction with CONFIG_LINKER_USE_ONDEMAND_SECTION and the
* K_MEM_MAP_UNPAGED flag to create demand mappings at boot time. This may
* also be used e.g. to implement file-based mmap().
*
* @param addr Virtual address to obtain a location token for
* @param [out] location storage location token
* @return 0 for success or negative error code
*/
int k_mem_paging_backing_store_location_query(void *addr, uintptr_t *location);
/**
* Copy a data page from K_MEM_SCRATCH_PAGE to the specified location
*

33
kernel/mmu.c
View file

@ -1050,6 +1050,34 @@ static void mark_linker_section_pinned(void *start_addr, void *end_addr,
}
#endif /* CONFIG_LINKER_USE_BOOT_SECTION) || CONFIG_LINKER_USE_PINNED_SECTION */
#ifdef CONFIG_LINKER_USE_ONDEMAND_SECTION
static void z_paging_ondemand_section_map(void)
{
uint8_t *addr;
size_t size;
uintptr_t location;
uint32_t flags;
size = (uintptr_t)lnkr_ondemand_text_size;
flags = K_MEM_MAP_UNPAGED | K_MEM_PERM_EXEC | K_MEM_CACHE_WB;
VIRT_FOREACH(lnkr_ondemand_text_start, size, addr) {
k_mem_paging_backing_store_location_query(addr, &location);
arch_mem_map(addr, location, CONFIG_MMU_PAGE_SIZE, flags);
sys_bitarray_set_region(&virt_region_bitmap, 1,
virt_to_bitmap_offset(addr, CONFIG_MMU_PAGE_SIZE));
}
size = (uintptr_t)lnkr_ondemand_rodata_size;
flags = K_MEM_MAP_UNPAGED | K_MEM_CACHE_WB;
VIRT_FOREACH(lnkr_ondemand_rodata_start, size, addr) {
k_mem_paging_backing_store_location_query(addr, &location);
arch_mem_map(addr, location, CONFIG_MMU_PAGE_SIZE, flags);
sys_bitarray_set_region(&virt_region_bitmap, 1,
virt_to_bitmap_offset(addr, CONFIG_MMU_PAGE_SIZE));
}
}
#endif /* CONFIG_LINKER_USE_ONDEMAND_SECTION */
void z_mem_manage_init(void)
{
uintptr_t phys;
@ -1126,6 +1154,11 @@ void z_mem_manage_init(void)
}
}
#endif /* CONFIG_DEMAND_PAGING */
#ifdef CONFIG_LINKER_USE_ONDEMAND_SECTION
z_paging_ondemand_section_map();
#endif
#if __ASSERT_ON
page_frames_initialized = true;
#endif