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Date: Wed, 19 Oct 2022 09:11:07 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Evgeniy Baskov <baskov@...ras.ru>
Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Alexey Khoroshilov <khoroshilov@...ras.ru>,
lvc-project@...uxtesting.org, x86@...nel.org,
linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH 05/16] x86/boot: Support 4KB pages for identity mapping
On Tue, 6 Sept 2022 at 12:42, Evgeniy Baskov <baskov@...ras.ru> 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@...ras.ru>
This looks reasonable to me but someone on team-x86 will need to review this.
One nit below
> ---
> 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
>
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