Re: [PATCH v6 22/24] mm: Speculative page fault handler return VMA

[Laurent Dufour]

On 13/01/2018 05:23, Matthew Wilcox wrote:
> On Fri, Jan 12, 2018 at 11:02:51AM -0800, Matthew Wilcox wrote:
>> On Fri, Jan 12, 2018 at 06:26:06PM +0100, Laurent Dufour wrote:
>>> @@ -1354,7 +1354,10 @@ extern int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>>>  		unsigned int flags);
>>>  #ifdef CONFIG_SPF
>>>  extern int handle_speculative_fault(struct mm_struct *mm,
>>> +				    unsigned long address, unsigned int flags,
>>> +				    struct vm_area_struct **vma);
>>
>> I think this shows that we need to create 'struct vm_fault' on the stack
>> in the arch code and then pass it to handle_speculative_fault(), followed
>> by handle_mm_fault().  That should be quite a nice cleanup actually.
>> I know that's only 30+ architectures to change ;-)
> 
> Of course, we don't need to change them all.  Try this:

That would be good candidate for a clean up but I'm not sure this should be
part of this already too long series.

If you don't mind, unless a global agreement is stated on that, I'd prefer
to postpone such a change once the initial series is accepted.

Cheers,
Laurent.

> Subject: [PATCH] Add vm_handle_fault
> 
> For the speculative fault handler, we want to create the struct vm_fault
> on the stack in the arch code and pass it into the generic mm code.
> To avoid changing 30+ architectures, leave handle_mm_fault with its
> current function signature and move its guts into the new vm_handle_fault
> function.  Even this saves a nice 172 bytes on the random x86-64 .config
> I happen to have around.
> 
> Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 5eb3d2524bdc..403934297a3d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3977,36 +3977,28 @@ static int handle_pte_fault(struct vm_fault *vmf)
>   * The mmap_sem may have been released depending on flags and our
>   * return value.  See filemap_fault() and __lock_page_or_retry().
>   */
> -static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> -		unsigned int flags)
> +static int __handle_mm_fault(struct vm_fault *vmf)
>  {
> -	struct vm_fault vmf = {
> -		.vma = vma,
> -		.address = address & PAGE_MASK,
> -		.flags = flags,
> -		.pgoff = linear_page_index(vma, address),
> -		.gfp_mask = __get_fault_gfp_mask(vma),
> -	};
> -	unsigned int dirty = flags & FAULT_FLAG_WRITE;
> -	struct mm_struct *mm = vma->vm_mm;
> +	unsigned int dirty = vmf->flags & FAULT_FLAG_WRITE;
> +	struct mm_struct *mm = vmf->vma->vm_mm;
>  	pgd_t *pgd;
>  	p4d_t *p4d;
>  	int ret;
> 
> -	pgd = pgd_offset(mm, address);
> -	p4d = p4d_alloc(mm, pgd, address);
> +	pgd = pgd_offset(mm, vmf->address);
> +	p4d = p4d_alloc(mm, pgd, vmf->address);
>  	if (!p4d)
>  		return VM_FAULT_OOM;
> 
> -	vmf.pud = pud_alloc(mm, p4d, address);
> -	if (!vmf.pud)
> +	vmf->pud = pud_alloc(mm, p4d, vmf->address);
> +	if (!vmf->pud)
>  		return VM_FAULT_OOM;
> -	if (pud_none(*vmf.pud) && transparent_hugepage_enabled(vma)) {
> -		ret = create_huge_pud(&vmf);
> +	if (pud_none(*vmf->pud) && transparent_hugepage_enabled(vmf->vma)) {
> +		ret = create_huge_pud(vmf);
>  		if (!(ret & VM_FAULT_FALLBACK))
>  			return ret;
>  	} else {
> -		pud_t orig_pud = *vmf.pud;
> +		pud_t orig_pud = *vmf->pud;
> 
>  		barrier();
>  		if (pud_trans_huge(orig_pud) || pud_devmap(orig_pud)) {
> @@ -4014,50 +4006,51 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  			/* NUMA case for anonymous PUDs would go here */
> 
>  			if (dirty && !pud_access_permitted(orig_pud, WRITE)) {
> -				ret = wp_huge_pud(&vmf, orig_pud);
> +				ret = wp_huge_pud(vmf, orig_pud);
>  				if (!(ret & VM_FAULT_FALLBACK))
>  					return ret;
>  			} else {
> -				huge_pud_set_accessed(&vmf, orig_pud);
> +				huge_pud_set_accessed(vmf, orig_pud);
>  				return 0;
>  			}
>  		}
>  	}
> 
> -	vmf.pmd = pmd_alloc(mm, vmf.pud, address);
> -	if (!vmf.pmd)
> +	vmf->pmd = pmd_alloc(mm, vmf->pud, vmf->address);
> +	if (!vmf->pmd)
>  		return VM_FAULT_OOM;
> -	if (pmd_none(*vmf.pmd) && transparent_hugepage_enabled(vma)) {
> -		ret = create_huge_pmd(&vmf);
> +	if (pmd_none(*vmf->pmd) && transparent_hugepage_enabled(vmf->vma)) {
> +		ret = create_huge_pmd(vmf);
>  		if (!(ret & VM_FAULT_FALLBACK))
>  			return ret;
>  	} else {
> -		pmd_t orig_pmd = *vmf.pmd;
> +		pmd_t orig_pmd = *vmf->pmd;
> 
>  		barrier();
>  		if (unlikely(is_swap_pmd(orig_pmd))) {
>  			VM_BUG_ON(thp_migration_supported() &&
>  					  !is_pmd_migration_entry(orig_pmd));
>  			if (is_pmd_migration_entry(orig_pmd))
> -				pmd_migration_entry_wait(mm, vmf.pmd);
> +				pmd_migration_entry_wait(mm, vmf->pmd);
>  			return 0;
>  		}
>  		if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
> -			if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
> -				return do_huge_pmd_numa_page(&vmf, orig_pmd);
> +			if (pmd_protnone(orig_pmd) &&
> +						vma_is_accessible(vmf->vma))
> +				return do_huge_pmd_numa_page(vmf, orig_pmd);
> 
>  			if (dirty && !pmd_access_permitted(orig_pmd, WRITE)) {
> -				ret = wp_huge_pmd(&vmf, orig_pmd);
> +				ret = wp_huge_pmd(vmf, orig_pmd);
>  				if (!(ret & VM_FAULT_FALLBACK))
>  					return ret;
>  			} else {
> -				huge_pmd_set_accessed(&vmf, orig_pmd);
> +				huge_pmd_set_accessed(vmf, orig_pmd);
>  				return 0;
>  			}
>  		}
>  	}
> 
> -	return handle_pte_fault(&vmf);
> +	return handle_pte_fault(vmf);
>  }
> 
>  /*
> @@ -4066,9 +4059,10 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>   * The mmap_sem may have been released depending on flags and our
>   * return value.  See filemap_fault() and __lock_page_or_retry().
>   */
> -int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> -		unsigned int flags)
> +int vm_handle_fault(struct vm_fault *vmf)
>  {
> +	unsigned int flags = vmf->flags;
> +	struct vm_area_struct *vma = vmf->vma;
>  	int ret;
> 
>  	__set_current_state(TASK_RUNNING);
> @@ -4092,9 +4086,9 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  		mem_cgroup_oom_enable();
> 
>  	if (unlikely(is_vm_hugetlb_page(vma)))
> -		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
> +		ret = hugetlb_fault(vma->vm_mm, vma, vmf->address, flags);
>  	else
> -		ret = __handle_mm_fault(vma, address, flags);
> +		ret = __handle_mm_fault(vmf);
> 
>  	if (flags & FAULT_FLAG_USER) {
>  		mem_cgroup_oom_disable();
> @@ -4110,6 +4104,26 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> 
>  	return ret;
>  }
> +
> +/*
> + * By the time we get here, we already hold the mm semaphore
> + *
> + * The mmap_sem may have been released depending on flags and our
> + * return value.  See filemap_fault() and __lock_page_or_retry().
> + */
> +int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> +		unsigned int flags)
> +{
> +	struct vm_fault vmf = {
> +		.vma = vma,
> +		.address = address & PAGE_MASK,
> +		.flags = flags,
> +		.pgoff = linear_page_index(vma, address),
> +		.gfp_mask = __get_fault_gfp_mask(vma),
> +	};
> +
> +	return vm_handle_fault(&vmf);
> +}
>  EXPORT_SYMBOL_GPL(handle_mm_fault);
> 
>  #ifndef __PAGETABLE_P4D_FOLDED
>