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x86: userspace: page in stack before starting user thread

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If generic section is not present at boot, the thread stack
may not be in physical memory. Unconditionally page in the stack
instead of relying on page fault to speed up a little bit
on starting the thread.

Also, this prevents a double fault during thread setup when
setting up stack permission in z_x86_userspace_enter().

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
This commit is contained in:
Daniel Leung 2021-07-15 12:52:21 -07:00 • committed by Christopher Friedt
commit 7605619c1e
1 changed files with 36 additions and 0 deletions
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36
arch/x86/core/userspace.c
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@ -106,6 +106,42 @@ FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
stack_end -= 8;
#endif
#if defined(CONFIG_DEMAND_PAGING) && \
!defined(CONFIG_LINKER_GENERIC_SECTIONS_PRESENT_AT_BOOT)
/* If generic section is not present at boot,
* the thread stack may not be in physical memory.
* Unconditionally page in the stack instead of
* relying on page fault to speed up a little bit
* on starting the thread.
*
* Note that this also needs to page in the reserved
* portion of the stack (which is usually the page just
* before the beginning of stack in
* _current->stack_info.start.
*/
uintptr_t stack_start;
size_t stack_size;
uintptr_t stack_aligned_start;
size_t stack_aligned_size;
stack_start = POINTER_TO_UINT(_current->stack_obj);
stack_size = Z_THREAD_STACK_SIZE_ADJUST(_current->stack_info.size);
#if defined(CONFIG_HW_STACK_PROTECTION)
/* With hardware stack protection, the first page of stack
* is a guard page. So need to skip it.
*/
stack_start += CONFIG_MMU_PAGE_SIZE;
stack_size -= CONFIG_MMU_PAGE_SIZE;
#endif
(void)k_mem_region_align(&stack_aligned_start, &stack_aligned_size,
stack_start, stack_size,
CONFIG_MMU_PAGE_SIZE);
k_mem_page_in(UINT_TO_POINTER(stack_aligned_start),
stack_aligned_size);
#endif
z_x86_userspace_enter(user_entry, p1, p2, p3, stack_end,
_current->stack_info.start);
CODE_UNREACHABLE;