[PATCHv2 3/4] x86/64/kexec: Map original relocate_kernel() in init_transition_pgtable()

Kirill A. Shutemov
2024-08-14T12:46:24Z

The init_transition_pgtable() function sets up transitional page tables.
It ensures that the relocate_kernel() function is present in the
identity mapping at the same location as in the kernel page tables.
relocate_kernel() switches to the identity mapping, and the function
must be present at the same location in the virtual address space before
and after switching page tables.

init_transition_pgtable() maps a copy of relocate_kernel() in
image->control_code_page at the relocate_kernel() virtual address, but
the original physical address of relocate_kernel() would also work.

It is safe to use original relocate_kernel() physical address cannot be
overwritten until swap_pages() is called, and the relocate_kernel()
virtual address will not be used by then.

Map the original relocate_kernel() at the relocate_kernel() virtual
address in the identity mapping. It is preparation to replace the
init_transition_pgtable() implementation with a call to
kernel_ident_mapping_init().

Note that while relocate_kernel() switches to the identity mapping, it
does not flush global TLB entries (CR4.PGE is not cleared). This means
that in most cases, the kernel still runs relocate_kernel() from the
original physical address before the change.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/kernel/machine_kexec_64.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 9c9ac606893e..645690e81c2d 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -157,7 +157,7 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
pte_t *pte;

vaddr = (unsigned long)relocate_kernel;
- paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);
+ paddr = __pa(relocate_kernel);
pgd += pgd_index(vaddr);
if (!pgd_present(*pgd)) {
p4d = (p4d_t *)get_zeroed_page(GFP_KERNEL);
--
2.43.0