[PATCH v30 04/11] arm64: mm: allow for unmapping memory region from kernel mapping

[panand@redhat.com (Pratyush Anand)]

On Tuesday 24 January 2017 02:19 PM, AKASHI Takahiro wrote:
> The current implementation of create_mapping_late() is only allowed
> to modify permission attributes (read-only or read-write) against
> the existing kernel mapping.
>
> In this patch, PAGE_KERNEL_INVALID protection attribute is introduced.
> We will now be able to invalidate (or unmap) some part of the existing
> kernel mapping by specifying PAGE_KERNEL_INVALID to create_mapping_late().
>
> This feature will be used in a suceeding kdump patch to protect
> the memory reserved for crash dump kernel once after loaded.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> ---
>  arch/arm64/include/asm/mmu.h           |  2 ++
>  arch/arm64/include/asm/pgtable-hwdef.h |  2 ++
>  arch/arm64/include/asm/pgtable-prot.h  |  1 +
>  arch/arm64/include/asm/pgtable.h       |  4 ++++
>  arch/arm64/mm/mmu.c                    | 29 ++++++++++++++++++++---------
>  5 files changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> index 47619411f0ff..a6c1367527bc 100644
> --- a/arch/arm64/include/asm/mmu.h
> +++ b/arch/arm64/include/asm/mmu.h
> @@ -36,6 +36,8 @@ extern void init_mem_pgprot(void);
>  extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
>  			       unsigned long virt, phys_addr_t size,
>  			       pgprot_t prot, bool page_mappings_only);
> +extern void create_mapping_late(phys_addr_t phys, unsigned long virt,
> +				phys_addr_t size, pgprot_t prot);
>  extern void *fixmap_remap_fdt(phys_addr_t dt_phys);
>
>  #endif
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index eb0c2bd90de9..e66efec31ca9 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -119,6 +119,7 @@
>  #define PUD_TABLE_BIT		(_AT(pgdval_t, 1) << 1)
>  #define PUD_TYPE_MASK		(_AT(pgdval_t, 3) << 0)
>  #define PUD_TYPE_SECT		(_AT(pgdval_t, 1) << 0)
> +#define PUD_VALID		PUD_TYPE_SECT
>
>  /*
>   * Level 2 descriptor (PMD).
> @@ -128,6 +129,7 @@
>  #define PMD_TYPE_TABLE		(_AT(pmdval_t, 3) << 0)
>  #define PMD_TYPE_SECT		(_AT(pmdval_t, 1) << 0)
>  #define PMD_TABLE_BIT		(_AT(pmdval_t, 1) << 1)
> +#define PMD_VALID		PMD_TYPE_SECT
>
>  /*
>   * Section
> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index 2142c7726e76..945d84cd5df7 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -54,6 +54,7 @@
>  #define PAGE_KERNEL_ROX		__pgprot(_PAGE_DEFAULT | PTE_UXN | PTE_DIRTY | PTE_RDONLY)
>  #define PAGE_KERNEL_EXEC	__pgprot(_PAGE_DEFAULT | PTE_UXN | PTE_DIRTY | PTE_WRITE)
>  #define PAGE_KERNEL_EXEC_CONT	__pgprot(_PAGE_DEFAULT | PTE_UXN | PTE_DIRTY | PTE_WRITE | PTE_CONT)
> +#define PAGE_KERNEL_INVALID	__pgprot(0)
>
>  #define PAGE_HYP		__pgprot(_PAGE_DEFAULT | PTE_HYP | PTE_HYP_XN)
>  #define PAGE_HYP_EXEC		__pgprot(_PAGE_DEFAULT | PTE_HYP | PTE_RDONLY)
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index ffbb9a520563..1904a7c07018 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -364,6 +364,8 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>
>  #define pmd_bad(pmd)		(!(pmd_val(pmd) & PMD_TABLE_BIT))
>
> +#define pmd_valid(pmd)		(!!(pmd_val(pmd) & PMD_VALID))
> +
>  #define pmd_table(pmd)		((pmd_val(pmd) & PMD_TYPE_MASK) == \
>  				 PMD_TYPE_TABLE)
>  #define pmd_sect(pmd)		((pmd_val(pmd) & PMD_TYPE_MASK) == \
> @@ -428,6 +430,7 @@ static inline phys_addr_t pmd_page_paddr(pmd_t pmd)
>
>  #define pud_none(pud)		(!pud_val(pud))
>  #define pud_bad(pud)		(!(pud_val(pud) & PUD_TABLE_BIT))
> +#define pud_valid(pud)		(!!(pud_val(pud) & PUD_VALID))

This will break compilation for CONFIG_PGTABLE_LEVELS <= 2

>  #define pud_present(pud)	(pud_val(pud))
>
>  static inline void set_pud(pud_t *pudp, pud_t pud)
> @@ -481,6 +484,7 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
>
>  #define pgd_none(pgd)		(!pgd_val(pgd))
>  #define pgd_bad(pgd)		(!(pgd_val(pgd) & 2))
> +#define pgd_valid(pgd)		(!!(pgd_val(pgd) & 1))

This has not been used anywhere.

>  #define pgd_present(pgd)	(pgd_val(pgd))
>
>  static inline void set_pgd(pgd_t *pgdp, pgd_t pgd)
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 17243e43184e..9c7adcce8e4e 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -133,7 +133,8 @@ static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
>  		 * Set the contiguous bit for the subsequent group of PTEs if
>  		 * its size and alignment are appropriate.
>  		 */
> -		if (((addr | PFN_PHYS(pfn)) & ~CONT_PTE_MASK) == 0) {
> +		if ((pgprot_val(prot) & PTE_VALID) &&
> +		    (((addr | PFN_PHYS(pfn)) & ~CONT_PTE_MASK) == 0)) {
>  			if (end - addr >= CONT_PTE_SIZE && !page_mappings_only)
>  				__prot = __pgprot(pgprot_val(prot) | PTE_CONT);
>  			else
> @@ -147,7 +148,8 @@ static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
>  		 * After the PTE entry has been populated once, we
>  		 * only allow updates to the permission attributes.
>  		 */
> -		BUG_ON(!pgattr_change_is_safe(pte_val(old_pte), pte_val(*pte)));
> +		BUG_ON(pte_valid(old_pte) && pte_valid(*pte) &&
> +		       !pgattr_change_is_safe(pte_val(old_pte), pte_val(*pte)));
>
>  	} while (pte++, addr += PAGE_SIZE, addr != end);
>
> @@ -190,7 +192,8 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
>  			 * Set the contiguous bit for the subsequent group of
>  			 * PMDs if its size and alignment are appropriate.
>  			 */
> -			if (((addr | phys) & ~CONT_PMD_MASK) == 0) {
> +			if ((pgprot_val(prot) | PMD_VALID) &&
> +			    ((addr | phys) & ~CONT_PMD_MASK) == 0) {
>  				if (end - addr >= CONT_PMD_SIZE)
>  					__prot = __pgprot(pgprot_val(prot) |
>  							  PTE_CONT);
> @@ -203,7 +206,8 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
>  			 * After the PMD entry has been populated once, we
>  			 * only allow updates to the permission attributes.
>  			 */
> -			BUG_ON(!pgattr_change_is_safe(pmd_val(old_pmd),
> +			BUG_ON(pmd_valid(old_pmd) && pmd_valid(*pmd) &&
> +			       !pgattr_change_is_safe(pmd_val(old_pmd),
>  						      pmd_val(*pmd)));
>  		} else {
>  			alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
> @@ -263,7 +267,8 @@ static void alloc_init_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
>  			 * After the PUD entry has been populated once, we
>  			 * only allow updates to the permission attributes.
>  			 */
> -			BUG_ON(!pgattr_change_is_safe(pud_val(old_pud),
> +			BUG_ON(pud_valid(old_pud) && pud_valid(*pud) &&
> +			       !pgattr_change_is_safe(pud_val(old_pud),
>  						      pud_val(*pud)));
>  		} else {
>  			alloc_init_pmd(pud, addr, next, phys, prot,
> @@ -344,8 +349,8 @@ void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
>  			     pgd_pgtable_alloc, page_mappings_only);
>  }
>
> -static void create_mapping_late(phys_addr_t phys, unsigned long virt,
> -				  phys_addr_t size, pgprot_t prot)
> +void create_mapping_late(phys_addr_t phys, unsigned long virt,
> +			 phys_addr_t size, pgprot_t prot)
>  {
>  	if (virt < VMALLOC_START) {
>  		pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
> @@ -791,14 +796,20 @@ int __init arch_ioremap_pmd_supported(void)
>  int pud_set_huge(pud_t *pud, phys_addr_t phys, pgprot_t prot)
>  {
>  	BUG_ON(phys & ~PUD_MASK);
> -	set_pud(pud, __pud(phys | PUD_TYPE_SECT | pgprot_val(mk_sect_prot(prot))));
> +	set_pud(pud, __pud(phys |
> +			   ((pgprot_val(prot) & PUD_VALID) ?
> +					PUD_TYPE_SECT : 0) |
> +			   pgprot_val(mk_sect_prot(prot))));
>  	return 1;
>  }
>
>  int pmd_set_huge(pmd_t *pmd, phys_addr_t phys, pgprot_t prot)
>  {
>  	BUG_ON(phys & ~PMD_MASK);
> -	set_pmd(pmd, __pmd(phys | PMD_TYPE_SECT | pgprot_val(mk_sect_prot(prot))));
> +	set_pmd(pmd, __pmd(phys |
> +			   ((pgprot_val(prot) & PMD_VALID) ?
> +					PMD_TYPE_SECT : 0) |
> +			   pgprot_val(mk_sect_prot(prot))));
>  	return 1;
>  }
>
>


~Pratyush