Re: [PATCH 2/9] mm: Add an apply_to_pfn_range interface

[Ralph Campbell <rcampbell@nvidia.com>]

On 4/12/19 9:04 AM, Thomas Hellstrom wrote:
> This is basically apply_to_page_range with added functionality:
> Allocating missing parts of the page table becomes optional, which
> means that the function can be guaranteed not to error if allocation
> is disabled. Also passing of the closure struct and callback function
> becomes different and more in line with how things are done elsewhere.
> 
> Finally we keep apply_to_page_range as a wrapper around apply_to_pfn_range
> 
> The reason for not using the page-walk code is that we want to perform
> the page-walk on vmas pointing to an address space without requiring the
> mmap_sem to be held rather thand on vmas belonging to a process with the

s/thand/than/

> mmap_sem held.
> 
> Notable changes since RFC:
> Don't export apply_to_pfn range.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Huang Ying <ying.huang@intel.com>
> Cc: Souptick Joarder <jrdr.linux@gmail.com>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>

Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>

> ---
>   include/linux/mm.h |  10 ++++
>   mm/memory.c        | 130 ++++++++++++++++++++++++++++++++++-----------
>   2 files changed, 108 insertions(+), 32 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 80bb6408fe73..b7dd4ddd6efb 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2632,6 +2632,16 @@ typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
>   extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>   			       unsigned long size, pte_fn_t fn, void *data);
>   
> +struct pfn_range_apply;
> +typedef int (*pter_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
> +			 struct pfn_range_apply *closure);
> +struct pfn_range_apply {
> +	struct mm_struct *mm;
> +	pter_fn_t ptefn;
> +	unsigned int alloc;
> +};
> +extern int apply_to_pfn_range(struct pfn_range_apply *closure,
> +			      unsigned long address, unsigned long size);
>   
>   #ifdef CONFIG_PAGE_POISONING
>   extern bool page_poisoning_enabled(void);
> diff --git a/mm/memory.c b/mm/memory.c
> index a95b4a3b1ae2..60d67158964f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1938,18 +1938,17 @@ int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long
>   }
>   EXPORT_SYMBOL(vm_iomap_memory);
>   
> -static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
> -				     unsigned long addr, unsigned long end,
> -				     pte_fn_t fn, void *data)
> +static int apply_to_pte_range(struct pfn_range_apply *closure, pmd_t *pmd,
> +			      unsigned long addr, unsigned long end)
>   {
>   	pte_t *pte;
>   	int err;
>   	pgtable_t token;
>   	spinlock_t *uninitialized_var(ptl);
>   
> -	pte = (mm == &init_mm) ?
> +	pte = (closure->mm == &init_mm) ?
>   		pte_alloc_kernel(pmd, addr) :
> -		pte_alloc_map_lock(mm, pmd, addr, &ptl);
> +		pte_alloc_map_lock(closure->mm, pmd, addr, &ptl);
>   	if (!pte)
>   		return -ENOMEM;
>   
> @@ -1960,86 +1959,107 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
>   	token = pmd_pgtable(*pmd);
>   
>   	do {
> -		err = fn(pte++, token, addr, data);
> +		err = closure->ptefn(pte++, token, addr, closure);
>   		if (err)
>   			break;
>   	} while (addr += PAGE_SIZE, addr != end);
>   
>   	arch_leave_lazy_mmu_mode();
>   
> -	if (mm != &init_mm)
> +	if (closure->mm != &init_mm)
>   		pte_unmap_unlock(pte-1, ptl);
>   	return err;
>   }
>   
> -static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
> -				     unsigned long addr, unsigned long end,
> -				     pte_fn_t fn, void *data)
> +static int apply_to_pmd_range(struct pfn_range_apply *closure, pud_t *pud,
> +			      unsigned long addr, unsigned long end)
>   {
>   	pmd_t *pmd;
>   	unsigned long next;
> -	int err;
> +	int err = 0;
>   
>   	BUG_ON(pud_huge(*pud));
>   
> -	pmd = pmd_alloc(mm, pud, addr);
> +	pmd = pmd_alloc(closure->mm, pud, addr);
>   	if (!pmd)
>   		return -ENOMEM;
> +
>   	do {
>   		next = pmd_addr_end(addr, end);
> -		err = apply_to_pte_range(mm, pmd, addr, next, fn, data);
> +		if (!closure->alloc && pmd_none_or_clear_bad(pmd))
> +			continue;
> +		err = apply_to_pte_range(closure, pmd, addr, next);
>   		if (err)
>   			break;
>   	} while (pmd++, addr = next, addr != end);
>   	return err;
>   }
>   
> -static int apply_to_pud_range(struct mm_struct *mm, p4d_t *p4d,
> -				     unsigned long addr, unsigned long end,
> -				     pte_fn_t fn, void *data)
> +static int apply_to_pud_range(struct pfn_range_apply *closure, p4d_t *p4d,
> +			      unsigned long addr, unsigned long end)
>   {
>   	pud_t *pud;
>   	unsigned long next;
> -	int err;
> +	int err = 0;
>   
> -	pud = pud_alloc(mm, p4d, addr);
> +	pud = pud_alloc(closure->mm, p4d, addr);
>   	if (!pud)
>   		return -ENOMEM;
> +
>   	do {
>   		next = pud_addr_end(addr, end);
> -		err = apply_to_pmd_range(mm, pud, addr, next, fn, data);
> +		if (!closure->alloc && pud_none_or_clear_bad(pud))
> +			continue;
> +		err = apply_to_pmd_range(closure, pud, addr, next);
>   		if (err)
>   			break;
>   	} while (pud++, addr = next, addr != end);
>   	return err;
>   }
>   
> -static int apply_to_p4d_range(struct mm_struct *mm, pgd_t *pgd,
> -				     unsigned long addr, unsigned long end,
> -				     pte_fn_t fn, void *data)
> +static int apply_to_p4d_range(struct pfn_range_apply *closure, pgd_t *pgd,
> +			      unsigned long addr, unsigned long end)
>   {
>   	p4d_t *p4d;
>   	unsigned long next;
> -	int err;
> +	int err = 0;
>   
> -	p4d = p4d_alloc(mm, pgd, addr);
> +	p4d = p4d_alloc(closure->mm, pgd, addr);
>   	if (!p4d)
>   		return -ENOMEM;
> +
>   	do {
>   		next = p4d_addr_end(addr, end);
> -		err = apply_to_pud_range(mm, p4d, addr, next, fn, data);
> +		if (!closure->alloc && p4d_none_or_clear_bad(p4d))
> +			continue;
> +		err = apply_to_pud_range(closure, p4d, addr, next);
>   		if (err)
>   			break;
>   	} while (p4d++, addr = next, addr != end);
>   	return err;
>   }
>   
> -/*
> - * Scan a region of virtual memory, filling in page tables as necessary
> - * and calling a provided function on each leaf page table.
> +/**
> + * apply_to_pfn_range - Scan a region of virtual memory, calling a provided
> + * function on each leaf page table entry
> + * @closure: Details about how to scan and what function to apply
> + * @addr: Start virtual address
> + * @size: Size of the region
> + *
> + * If @closure->alloc is set to 1, the function will fill in the page table
> + * as necessary. Otherwise it will skip non-present parts.
> + * Note: The caller must ensure that the range does not contain huge pages.
> + * The caller must also assure that the proper mmu_notifier functions are
> + * called. Either in the pte leaf function or before and after the call to
> + * apply_to_pfn_range.
> + *
> + * Returns: Zero on success. If the provided function returns a non-zero status,

s/Returns/Return/
See Documentation/kernel-guide/kernel-doc.rst

> + * the page table walk will terminate and that status will be returned.
> + * If @closure->alloc is set to 1, then this function may also return memory
> + * allocation errors arising from allocating page table memory.
>    */
> -int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
> -			unsigned long size, pte_fn_t fn, void *data)
> +int apply_to_pfn_range(struct pfn_range_apply *closure,
> +		       unsigned long addr, unsigned long size)
>   {
>   	pgd_t *pgd;
>   	unsigned long next;
> @@ -2049,16 +2069,62 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
>   	if (WARN_ON(addr >= end))
>   		return -EINVAL;
>   
> -	pgd = pgd_offset(mm, addr);
> +	pgd = pgd_offset(closure->mm, addr);
>   	do {
>   		next = pgd_addr_end(addr, end);
> -		err = apply_to_p4d_range(mm, pgd, addr, next, fn, data);
> +		if (!closure->alloc && pgd_none_or_clear_bad(pgd))
> +			continue;
> +		err = apply_to_p4d_range(closure, pgd, addr, next);
>   		if (err)
>   			break;
>   	} while (pgd++, addr = next, addr != end);
>   
>   	return err;
>   }
> +
> +/**
> + * struct page_range_apply - Closure structure for apply_to_page_range()
> + * @pter: The base closure structure we derive from
> + * @fn: The leaf pte function to call
> + * @data: The leaf pte function closure
> + */
> +struct page_range_apply {
> +	struct pfn_range_apply pter;
> +	pte_fn_t fn;
> +	void *data;
> +};
> +
> +/*
> + * Callback wrapper to enable use of apply_to_pfn_range for
> + * the apply_to_page_range interface
> + */
> +static int apply_to_page_range_wrapper(pte_t *pte, pgtable_t token,
> +				       unsigned long addr,
> +				       struct pfn_range_apply *pter)
> +{
> +	struct page_range_apply *pra =
> +		container_of(pter, typeof(*pra), pter);
> +
> +	return pra->fn(pte, token, addr, pra->data);
> +}
> +
> +/*
> + * Scan a region of virtual memory, filling in page tables as necessary
> + * and calling a provided function on each leaf page table.
> + */
> +int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
> +			unsigned long size, pte_fn_t fn, void *data)
> +{
> +	struct page_range_apply pra = {
> +		.pter = {.mm = mm,
> +			 .alloc = 1,
> +			 .ptefn = apply_to_page_range_wrapper },
> +		.fn = fn,
> +		.data = data
> +	};
> +
> +	return apply_to_pfn_range(&pra.pter, addr, size);
> +}
>   EXPORT_SYMBOL_GPL(apply_to_page_range);
>   
>   /*
>