| Message ID | 20190925121833.2766-1-richardw.yang@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] userfaultfd: remove one unnecessary warn_on in __mcopy_atomic_hugetlb | expand |
On 9/25/19 5:18 AM, Wei Yang wrote: > The warning here is to make sure address(dst_addr) and length(len - > copied) are huge page size aligned. > > While this is ensured by: > > dst_start and len is huge page size aligned > dst_addr equals to dst_start and increase huge page size each time > copied increase huge page size each time Can we also remove the following for the same reasons? diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 640ff2bd9a69..f82d5ec698d8 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -262,7 +262,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, pte_t dst_pteval; BUG_ON(dst_addr >= dst_start + len); - VM_BUG_ON(dst_addr & ~huge_page_mask(h)); /* * Serialize via hugetlb_fault_mutex
On Wed, Sep 25, 2019 at 10:44:58AM -0700, Mike Kravetz wrote: >On 9/25/19 5:18 AM, Wei Yang wrote: >> The warning here is to make sure address(dst_addr) and length(len - >> copied) are huge page size aligned. >> >> While this is ensured by: >> >> dst_start and len is huge page size aligned >> dst_addr equals to dst_start and increase huge page size each time >> copied increase huge page size each time > >Can we also remove the following for the same reasons? > >diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >index 640ff2bd9a69..f82d5ec698d8 100644 >--- a/mm/userfaultfd.c >+++ b/mm/userfaultfd.c >@@ -262,7 +262,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, > pte_t dst_pteval; > > BUG_ON(dst_addr >= dst_start + len); >- VM_BUG_ON(dst_addr & ~huge_page_mask(h)); > Thanks for your comment. It looks good, while I lack some knowledge between vma_hpagesize and huge_page_mask(). If they are the same, why not use the same interface for all those checks in this function? > /* > * Serialize via hugetlb_fault_mutex > >-- >Mike Kravetz > >> >> This means this warning will never be triggered. >> >> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com> >> --- >> mm/userfaultfd.c | 4 ---- >> 1 file changed, 4 deletions(-) >> >> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >> index c7ae74ce5ff3..7895c715000e 100644 >> --- a/mm/userfaultfd.c >> +++ b/mm/userfaultfd.c >> @@ -243,10 +243,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, >> vm_shared = dst_vma->vm_flags & VM_SHARED; >> } >> >> - if (WARN_ON(dst_addr & (vma_hpagesize - 1) || >> - (len - copied) & (vma_hpagesize - 1))) >> - goto out_unlock; >> - >> /* >> * If not shared, ensure the dst_vma has a anon_vma. >> */ >>
On 9/25/19 5:35 PM, Wei Yang wrote: > On Wed, Sep 25, 2019 at 10:44:58AM -0700, Mike Kravetz wrote: >> On 9/25/19 5:18 AM, Wei Yang wrote: >>> The warning here is to make sure address(dst_addr) and length(len - >>> copied) are huge page size aligned. >>> >>> While this is ensured by: >>> >>> dst_start and len is huge page size aligned >>> dst_addr equals to dst_start and increase huge page size each time >>> copied increase huge page size each time >> >> Can we also remove the following for the same reasons? >> >> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >> index 640ff2bd9a69..f82d5ec698d8 100644 >> --- a/mm/userfaultfd.c >> +++ b/mm/userfaultfd.c >> @@ -262,7 +262,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, >> pte_t dst_pteval; >> >> BUG_ON(dst_addr >= dst_start + len); >> - VM_BUG_ON(dst_addr & ~huge_page_mask(h)); >> > > Thanks for your comment. > > It looks good, while I lack some knowledge between vma_hpagesize and > huge_page_mask(). vma_hpagesize is just a local variable used so that repeated calls to vma_kernel_pagesize() or huge_page_size() are not necessary. > If they are the same, why not use the same interface for all those checks in > this function? If we remove the VM_BUG_ON, that is the only use of huge_page_mask() in the function. We can can also eliminate a call to huge_page_size() by making this change. @@ -273,7 +272,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, mutex_lock(&hugetlb_fault_mutex_table[hash]); err = -ENOMEM; - dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h)); + dst_pte = huge_pte_alloc(dst_mm, dst_addr, vma_hpagesize); if (!dst_pte) { mutex_unlock(&hugetlb_fault_mutex_table[hash]); goto out_unlock;
On Wed, Sep 25, 2019 at 07:10:46PM -0700, Mike Kravetz wrote: >On 9/25/19 5:35 PM, Wei Yang wrote: >> On Wed, Sep 25, 2019 at 10:44:58AM -0700, Mike Kravetz wrote: >>> On 9/25/19 5:18 AM, Wei Yang wrote: >>>> The warning here is to make sure address(dst_addr) and length(len - >>>> copied) are huge page size aligned. >>>> >>>> While this is ensured by: >>>> >>>> dst_start and len is huge page size aligned >>>> dst_addr equals to dst_start and increase huge page size each time >>>> copied increase huge page size each time >>> >>> Can we also remove the following for the same reasons? >>> >>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >>> index 640ff2bd9a69..f82d5ec698d8 100644 >>> --- a/mm/userfaultfd.c >>> +++ b/mm/userfaultfd.c >>> @@ -262,7 +262,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, >>> pte_t dst_pteval; >>> >>> BUG_ON(dst_addr >= dst_start + len); >>> - VM_BUG_ON(dst_addr & ~huge_page_mask(h)); >>> >> >> Thanks for your comment. >> >> It looks good, while I lack some knowledge between vma_hpagesize and >> huge_page_mask(). > >vma_hpagesize is just a local variable used so that repeated calls to >vma_kernel_pagesize() or huge_page_size() are not necessary. > Thanks for your confirmation. If this is the case, we can remove this BUG_ON safely. >> If they are the same, why not use the same interface for all those checks in >> this function? > >If we remove the VM_BUG_ON, that is the only use of huge_page_mask() in >the function. > >We can can also eliminate a call to huge_page_size() by making this change. > >@@ -273,7 +272,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, > mutex_lock(&hugetlb_fault_mutex_table[hash]); > > err = -ENOMEM; >- dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h)); >+ dst_pte = huge_pte_alloc(dst_mm, dst_addr, vma_hpagesize); > if (!dst_pte) { > mutex_unlock(&hugetlb_fault_mutex_table[hash]); > goto out_unlock; Agree, and also with this I think diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index c153344774c7..74363f0a0dd0 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -315,7 +315,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, err = copy_huge_page_from_user(page, (const void __user *)src_addr, - pages_per_huge_page(h), true); + vma_hpagesize / PAGE_SIZE, true); if (unlikely(err)) { err = -EFAULT; goto out; After these cleanup, we use vma_pagesize to deal with all page size related calculation in this function, which looks more consistent to me. Does it looks good to you? >-- >Mike Kravetz
On 9/25/19 7:56 PM, Wei Yang wrote: > On Wed, Sep 25, 2019 at 07:10:46PM -0700, Mike Kravetz wrote: >> On 9/25/19 5:35 PM, Wei Yang wrote: >>> On Wed, Sep 25, 2019 at 10:44:58AM -0700, Mike Kravetz wrote: >>>> On 9/25/19 5:18 AM, Wei Yang wrote: >>>>> The warning here is to make sure address(dst_addr) and length(len - >>>>> copied) are huge page size aligned. >>>>> >>>>> While this is ensured by: >>>>> >>>>> dst_start and len is huge page size aligned >>>>> dst_addr equals to dst_start and increase huge page size each time >>>>> copied increase huge page size each time >>>> >>>> Can we also remove the following for the same reasons? >>>> >>>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >>>> index 640ff2bd9a69..f82d5ec698d8 100644 >>>> --- a/mm/userfaultfd.c >>>> +++ b/mm/userfaultfd.c >>>> @@ -262,7 +262,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, >>>> pte_t dst_pteval; >>>> >>>> BUG_ON(dst_addr >= dst_start + len); >>>> - VM_BUG_ON(dst_addr & ~huge_page_mask(h)); >>>> >>> >>> Thanks for your comment. >>> >>> It looks good, while I lack some knowledge between vma_hpagesize and >>> huge_page_mask(). >> >> vma_hpagesize is just a local variable used so that repeated calls to >> vma_kernel_pagesize() or huge_page_size() are not necessary. >> > > Thanks for your confirmation. If this is the case, we can remove this BUG_ON > safely. > >>> If they are the same, why not use the same interface for all those checks in >>> this function? >> >> If we remove the VM_BUG_ON, that is the only use of huge_page_mask() in >> the function. >> >> We can can also eliminate a call to huge_page_size() by making this change. >> >> @@ -273,7 +272,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, >> mutex_lock(&hugetlb_fault_mutex_table[hash]); >> >> err = -ENOMEM; >> - dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h)); >> + dst_pte = huge_pte_alloc(dst_mm, dst_addr, vma_hpagesize); >> if (!dst_pte) { >> mutex_unlock(&hugetlb_fault_mutex_table[hash]); >> goto out_unlock; > > Agree, and also with this I think > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index c153344774c7..74363f0a0dd0 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -315,7 +315,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, > > err = copy_huge_page_from_user(page, > (const void __user *)src_addr, > - pages_per_huge_page(h), true); > + vma_hpagesize / PAGE_SIZE, true); > if (unlikely(err)) { > err = -EFAULT; > goto out; > > After these cleanup, we use vma_pagesize to deal with all page size related > calculation in this function, which looks more consistent to me. > > Does it looks good to you? Yes, that looks good. Thanks for cleaning up this code.
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index c7ae74ce5ff3..7895c715000e 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -243,10 +243,6 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, vm_shared = dst_vma->vm_flags & VM_SHARED; } - if (WARN_ON(dst_addr & (vma_hpagesize - 1) || - (len - copied) & (vma_hpagesize - 1))) - goto out_unlock; - /* * If not shared, ensure the dst_vma has a anon_vma. */
The warning here is to make sure address(dst_addr) and length(len - copied) are huge page size aligned. While this is ensured by: dst_start and len is huge page size aligned dst_addr equals to dst_start and increase huge page size each time copied increase huge page size each time This means this warning will never be triggered. Signed-off-by: Wei Yang <richardw.yang@linux.intel.com> --- mm/userfaultfd.c | 4 ---- 1 file changed, 4 deletions(-)