On Wed, Jul 03, 2024 at 11:06:21AM +0000, Huang, Kai wrote:
> > static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
> > {
> > - pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> > - unsigned long vaddr, paddr;
> > - int result = -ENOMEM;
> > - p4d_t *p4d;
> > - pud_t *pud;
> > - pmd_t *pmd;
> > - pte_t *pte;
> > + struct x86_mapping_info info = {
> > + .alloc_pgt_page = alloc_transition_pgt_page,
> > + .context = image,
> > + .page_flag = __PAGE_KERNEL_LARGE_EXEC,
> > + .kernpg_flag = _KERNPG_TABLE_NOENC,
> > + .offset = __START_KERNEL_map - phys_base,
> > + };
> > + unsigned long mstart = PAGE_ALIGN_DOWN(__pa(relocate_kernel));
> > + unsigned long mend = mstart + PAGE_SIZE;
> >
> > - vaddr = (unsigned long)relocate_kernel;
> > - paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);
>
> Perhaps I am missing something, but this seems a functional change to me.
>
> IIUC the page after image->control_code_page is allocated when loading the
> kexec kernel image. It is a different page from the page where the
> relocate_kernel code resides in.
>
> The old code maps relocate_kernel kernel VA to the page after the
> control_code_page. Later in machine_kexec(), the relocate_kernel code is
> copied to that page so the mapping can work for that:
>
> control_page = page_address(image->control_code_page) + PAGE_SIZE;
> __memcpy(control_page, relocate_kernel,
> KEXEC_CONTROL_CODE_MAX_SIZE);
>
> The new code in this patch, however, seems just maps the relocate_kernel VA
> to the PA of the relocate_kernel, which should be different from the old
> mapping.
Yes, original code maps at relocate_kernel() VA the page with copy of the
relocate_kernel() in control_code_page. But it is safe to map original
relocate_kernel() page there as well as it is not going to be overwritten
until swap_pages(). We are not going to use original relocate_kernel()
page after RET at the end of relocate_kernel().
Does it make any sense?
I will try to explain it in the commit message in the next version.
--
Kiryl Shutsemau / Kirill A. Shutemov
