| Message ID | 20240701124334.1855981-4-kirill.shutemov@linux.intel.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere, archived |
| Headers | show |
| Series | x86: Reduce code duplication on page table initialization | expand |
On Mon, 2024-07-01 at 15:43 +0300, Kirill A. Shutemov wrote: > init_transition_pgtable() setups transitional page tables. Rewrite it > using kernel_ident_mapping_init() to avoid code duplication. setups -> sets up > > struct kimage_arch changed to track allocated page tables as a list, not > linking them to specific page table levels. This doesn't look like imperative mode. Perhaps change to: Change struct kimage_arch to track ... [...] > 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.
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.
On Thu, 2024-07-04 at 16:44 +0300, kirill.shutemov@linux.intel.com wrote: > 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(). I am not super familiar with this, but this doesn't seem 100% safe to me. E.g, did you consider the kexec jump case? The second half of control page is also used to store registers in kexec jump. If the relocate_kernel VA isn't mapped to the control page, then IIUC after jumping back to old kernel it seems we won't be able to read those registers back? > > Does it make any sense? > > I will try to explain it in the commit message in the next version. > I think even it's safe to change to map to the relocate_kernel() page, it should be done in a separate patch. This patch should just focus on removing the duplicated page table setup code.
diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h index ae5482a2f0ca..7f9287f371e6 100644 --- a/arch/x86/include/asm/kexec.h +++ b/arch/x86/include/asm/kexec.h @@ -145,10 +145,7 @@ struct kimage_arch { }; #else struct kimage_arch { - p4d_t *p4d; - pud_t *pud; - pmd_t *pmd; - pte_t *pte; + struct list_head pages; }; #endif /* CONFIG_X86_32 */ diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c index cc0f7f70b17b..951b17d217ab 100644 --- a/arch/x86/kernel/machine_kexec_64.c +++ b/arch/x86/kernel/machine_kexec_64.c @@ -107,71 +107,42 @@ map_efi_systab(struct x86_mapping_info *info, pgd_t *level4p) return 0; } +static void *alloc_transition_pgt_page(void *data) +{ + struct kimage *image = (struct kimage *)data; + unsigned long virt; + + virt = get_zeroed_page(GFP_KERNEL); + if (!virt) + return NULL; + + list_add(&virt_to_page(virt)->lru, &image->arch.pages); + return (void *)virt; +} + static void free_transition_pgtable(struct kimage *image) { - free_page((unsigned long)image->arch.p4d); - image->arch.p4d = NULL; - free_page((unsigned long)image->arch.pud); - image->arch.pud = NULL; - free_page((unsigned long)image->arch.pmd); - image->arch.pmd = NULL; - free_page((unsigned long)image->arch.pte); - image->arch.pte = NULL; + struct page *page, *tmp; + + list_for_each_entry_safe(page, tmp, &image->arch.pages, lru) { + list_del(&page->lru); + free_page((unsigned long)page_address(page)); + } } 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); - pgd += pgd_index(vaddr); - if (!pgd_present(*pgd)) { - p4d = (p4d_t *)get_zeroed_page(GFP_KERNEL); - if (!p4d) - goto err; - image->arch.p4d = p4d; - set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE)); - } - p4d = p4d_offset(pgd, vaddr); - if (!p4d_present(*p4d)) { - pud = (pud_t *)get_zeroed_page(GFP_KERNEL); - if (!pud) - goto err; - image->arch.pud = pud; - set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE)); - } - pud = pud_offset(p4d, vaddr); - if (!pud_present(*pud)) { - pmd = (pmd_t *)get_zeroed_page(GFP_KERNEL); - if (!pmd) - goto err; - image->arch.pmd = pmd; - set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE)); - } - pmd = pmd_offset(pud, vaddr); - if (!pmd_present(*pmd)) { - pte = (pte_t *)get_zeroed_page(GFP_KERNEL); - if (!pte) - goto err; - image->arch.pte = pte; - set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE)); - } - pte = pte_offset_kernel(pmd, vaddr); - - if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) - prot = PAGE_KERNEL_EXEC; - - set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot)); - return 0; -err: - return result; + return kernel_ident_mapping_init(&info, pgd, mstart, mend); } static void *alloc_pgt_page(void *data) @@ -272,6 +243,8 @@ int machine_kexec_prepare(struct kimage *image) unsigned long start_pgtable; int result; + INIT_LIST_HEAD(&image->arch.pages); + /* Calculate the offsets */ start_pgtable = page_to_pfn(image->control_code_page) << PAGE_SHIFT;
init_transition_pgtable() setups transitional page tables. Rewrite it using kernel_ident_mapping_init() to avoid code duplication. struct kimage_arch changed to track allocated page tables as a list, not linking them to specific page table levels. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- arch/x86/include/asm/kexec.h | 5 +- arch/x86/kernel/machine_kexec_64.c | 89 +++++++++++------------------- 2 files changed, 32 insertions(+), 62 deletions(-)