Re: [PATCH 05/16] x86/boot: Support 4KB pages for identity mapping
From: Evgeniy Baskov
Date: Thu Oct 20 2022 - 07:30:57 EST
On 2022-10-19 10:11, Ard Biesheuvel wrote:
On Tue, 6 Sept 2022 at 12:42, Evgeniy Baskov <baskov@xxxxxxxxx> wrote:
Current identity mapping code only supports 2M and 1G pages.
4KB pages are desirable for better memory protection granularity
in compressed kernel code.
Change identity mapping code to support 4KB pages and
memory remapping with different attributes.
Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
This looks reasonable to me but someone on team-x86 will need to review
this.
One nit below
Thanks!
---
arch/x86/include/asm/init.h | 1 +
arch/x86/mm/ident_map.c | 186
+++++++++++++++++++++++++++++-------
2 files changed, 155 insertions(+), 32 deletions(-)
diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
index 5f1d3c421f68..a8277ee82c51 100644
--- a/arch/x86/include/asm/init.h
+++ b/arch/x86/include/asm/init.h
@@ -8,6 +8,7 @@ struct x86_mapping_info {
unsigned long page_flag; /* page flag for PMD or PUD
entry */
unsigned long offset; /* ident mapping offset */
bool direct_gbpages; /* PUD level 1GB page support
*/
+ bool allow_4kpages; /* Allow more granular
mappings with 4K pages */
unsigned long kernpg_flag; /* kernel pagetable flag
override */
};
diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
index 968d7005f4a7..ad455d4ef595 100644
--- a/arch/x86/mm/ident_map.c
+++ b/arch/x86/mm/ident_map.c
@@ -2,26 +2,130 @@
/*
* Helper routines for building identity mapping page tables. This is
* included by both the compressed kernel and the regular kernel.
+ *
Drop this change
*/
-static void ident_pmd_init(struct x86_mapping_info *info, pmd_t
*pmd_page,
- unsigned long addr, unsigned long end)
+static void ident_pte_init(struct x86_mapping_info *info, pte_t
*pte_page,
+ unsigned long addr, unsigned long end,
+ unsigned long flags)
{
- addr &= PMD_MASK;
- for (; addr < end; addr += PMD_SIZE) {
+ addr &= PAGE_MASK;
+ for (; addr < end; addr += PAGE_SIZE) {
+ pte_t *pte = pte_page + pte_index(addr);
+
+ set_pte(pte, __pte((addr - info->offset) | flags));
+ }
+}
+
+pte_t *ident_split_large_pmd(struct x86_mapping_info *info,
+ pmd_t *pmdp, unsigned long page_addr)
+{
+ unsigned long pmd_addr, page_flags;
+ pte_t *pte;
+
+ pte = (pte_t *)info->alloc_pgt_page(info->context);
+ if (!pte)
+ return NULL;
+
+ pmd_addr = page_addr & PMD_MASK;
+
+ /* Not a large page - clear PSE flag */
+ page_flags = pmd_flags(*pmdp) & ~_PSE;
+ ident_pte_init(info, pte, pmd_addr, pmd_addr + PMD_SIZE,
page_flags);
+
+ return pte;
+}
+
+static int ident_pmd_init(struct x86_mapping_info *info, pmd_t
*pmd_page,
+ unsigned long addr, unsigned long end,
+ unsigned long flags)
+{
+ unsigned long next;
+ bool new_table = 0;
+
+ for (; addr < end; addr = next) {
pmd_t *pmd = pmd_page + pmd_index(addr);
+ pte_t *pte;
- if (pmd_present(*pmd))
+ next = (addr & PMD_MASK) + PMD_SIZE;
+ if (next > end)
+ next = end;
+
+ /*
+ * Use 2M pages if 4k pages are not allowed or
+ * we are not mapping extra, i.e. address and size are
aligned.
+ */
+
+ if (!info->allow_4kpages ||
+ (!(addr & ~PMD_MASK) && next == addr + PMD_SIZE))
{
+
+ pmd_t pmdval;
+
+ addr &= PMD_MASK;
+ pmdval = __pmd((addr - info->offset) | flags |
_PSE);
+ set_pmd(pmd, pmdval);
continue;
+ }
+
+ /*
+ * If currently mapped page is large, we need to split
it.
+ * The case when we can remap 2M page to 2M page
+ * with different flags is already covered above.
+ *
+ * If there's nothing mapped to desired address,
+ * we need to allocate new page table.
+ */
- set_pmd(pmd, __pmd((addr - info->offset) |
info->page_flag));
+ if (pmd_large(*pmd)) {
+ pte = ident_split_large_pmd(info, pmd, addr);
+ new_table = 1;
+ } else if (!pmd_present(*pmd)) {
+ pte = (pte_t
*)info->alloc_pgt_page(info->context);
+ new_table = 1;
+ } else {
+ pte = pte_offset_kernel(pmd, 0);
+ new_table = 0;
+ }
+
+ if (!pte)
+ return -ENOMEM;
+
+ ident_pte_init(info, pte, addr, next, flags);
+
+ if (new_table)
+ set_pmd(pmd, __pmd(__pa(pte) |
info->kernpg_flag));
}
+
+ return 0;
}
+
+pmd_t *ident_split_large_pud(struct x86_mapping_info *info,
+ pud_t *pudp, unsigned long page_addr)
+{
+ unsigned long pud_addr, page_flags;
+ pmd_t *pmd;
+
+ pmd = (pmd_t *)info->alloc_pgt_page(info->context);
+ if (!pmd)
+ return NULL;
+
+ pud_addr = page_addr & PUD_MASK;
+
+ /* Not a large page - clear PSE flag */
+ page_flags = pud_flags(*pudp) & ~_PSE;
+ ident_pmd_init(info, pmd, pud_addr, pud_addr + PUD_SIZE,
page_flags);
+
+ return pmd;
+}
+
+
static int ident_pud_init(struct x86_mapping_info *info, pud_t
*pud_page,
unsigned long addr, unsigned long end)
{
unsigned long next;
+ bool new_table = 0;
+ int result;
for (; addr < end; addr = next) {
pud_t *pud = pud_page + pud_index(addr);
@@ -31,28 +135,39 @@ static int ident_pud_init(struct x86_mapping_info
*info, pud_t *pud_page,
if (next > end)
next = end;
+ /* Use 1G pages only if forced, even if they are
supported. */
if (info->direct_gbpages) {
pud_t pudval;
-
- if (pud_present(*pud))
- continue;
+ unsigned long flags;
addr &= PUD_MASK;
- pudval = __pud((addr - info->offset) |
info->page_flag);
+ flags = info->page_flag | _PSE;
+ pudval = __pud((addr - info->offset) | flags);
+
set_pud(pud, pudval);
continue;
}
- if (pud_present(*pud)) {
+ if (pud_large(*pud)) {
+ pmd = ident_split_large_pud(info, pud, addr);
+ new_table = 1;
+ } else if (!pud_present(*pud)) {
+ pmd = (pmd_t
*)info->alloc_pgt_page(info->context);
+ new_table = 1;
+ } else {
pmd = pmd_offset(pud, 0);
- ident_pmd_init(info, pmd, addr, next);
- continue;
+ new_table = 0;
}
- pmd = (pmd_t *)info->alloc_pgt_page(info->context);
+
if (!pmd)
return -ENOMEM;
- ident_pmd_init(info, pmd, addr, next);
- set_pud(pud, __pud(__pa(pmd) | info->kernpg_flag));
+
+ result = ident_pmd_init(info, pmd, addr, next,
info->page_flag);
+ if (result)
+ return result;
+
+ if (new_table)
+ set_pud(pud, __pud(__pa(pmd) |
info->kernpg_flag));
}
return 0;
@@ -63,6 +178,7 @@ static int ident_p4d_init(struct x86_mapping_info
*info, p4d_t *p4d_page,
{
unsigned long next;
int result;
+ bool new_table = 0;
for (; addr < end; addr = next) {
p4d_t *p4d = p4d_page + p4d_index(addr);
@@ -72,15 +188,14 @@ static int ident_p4d_init(struct x86_mapping_info
*info, p4d_t *p4d_page,
if (next > end)
next = end;
- if (p4d_present(*p4d)) {
+ if (!p4d_present(*p4d)) {
+ pud = (pud_t
*)info->alloc_pgt_page(info->context);
+ new_table = 1;
+ } else {
pud = pud_offset(p4d, 0);
- result = ident_pud_init(info, pud, addr,
next);
- if (result)
- return result;
-
- continue;
+ new_table = 0;
}
- pud = (pud_t *)info->alloc_pgt_page(info->context);
+
if (!pud)
return -ENOMEM;
@@ -88,19 +203,22 @@ static int ident_p4d_init(struct x86_mapping_info
*info, p4d_t *p4d_page,
if (result)
return result;
- set_p4d(p4d, __p4d(__pa(pud) | info->kernpg_flag));
+ if (new_table)
+ set_p4d(p4d, __p4d(__pa(pud) |
info->kernpg_flag));
}
return 0;
}
-int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t
*pgd_page,
- unsigned long pstart, unsigned long
pend)
+int kernel_ident_mapping_init(struct x86_mapping_info *info,
+ pgd_t *pgd_page, unsigned long pstart,
+ unsigned long pend)
{
unsigned long addr = pstart + info->offset;
unsigned long end = pend + info->offset;
unsigned long next;
int result;
+ bool new_table;
/* Set the default pagetable flags if not supplied */
if (!info->kernpg_flag)
@@ -117,20 +235,24 @@ int kernel_ident_mapping_init(struct
x86_mapping_info *info, pgd_t *pgd_page,
if (next > end)
next = end;
- if (pgd_present(*pgd)) {
+ if (!pgd_present(*pgd)) {
+ p4d = (p4d_t
*)info->alloc_pgt_page(info->context);
+ new_table = 1;
+ } else {
p4d = p4d_offset(pgd, 0);
- result = ident_p4d_init(info, p4d, addr,
next);
- if (result)
- return result;
- continue;
+ new_table = 0;
}
- p4d = (p4d_t *)info->alloc_pgt_page(info->context);
if (!p4d)
return -ENOMEM;
+
result = ident_p4d_init(info, p4d, addr, next);
if (result)
return result;
+
+ if (!new_table)
+ continue;
+
if (pgtable_l5_enabled()) {
set_pgd(pgd, __pgd(__pa(p4d) |
info->kernpg_flag));
} else {
--
2.35.1