| Message ID | 20210120173612.20913-5-will@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Create 'old' ptes for faultaround mappings on arm64 with hardware access flag | expand |
On Wed, Jan 20, 2021 at 9:36 AM Will Deacon <will@kernel.org> wrote: > > 'struct vm_fault' contains both information about the fault being > serviced alongside mutable fields contributing to the state of the > fault-handling logic. Unfortunately, the distinction between the two is > not clear-cut, and a number of callers end up manipulating the structure > temporarily before restoring it when returning. > > Try to clean this up by moving the immutable fault information into an > anonymous struct, which will later be marked as 'const'. GCC will then > complain (with an error) about modification of these fields after they > have been initialised, although LLVM currently allows them without even > a warning: > > https://bugs.llvm.org/show_bug.cgi?id=48755 I think this paragraph+link would be better on patch 8/8. > > Ideally, the 'flags' field would be part of the new structure too, but > it seems as though the ->page_mkwrite() path is not ready for this yet. > > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> > Link: https://lore.kernel.org/r/CAHk-=whYs9XsO88iqJzN6NC=D-dp2m0oYXuOoZ=eWnvv=5OA+w@mail.gmail.com > Signed-off-by: Will Deacon <will@kernel.org> > --- > include/linux/mm.h | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 251a2339befb..b4a5cb9bff7d 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -517,11 +517,14 @@ static inline bool fault_flag_allow_retry_first(unsigned int flags) > * pgoff should be used in favour of virtual_address, if possible. > */ > struct vm_fault { > - struct vm_area_struct *vma; /* Target VMA */ > - unsigned int flags; /* FAULT_FLAG_xxx flags */ > - gfp_t gfp_mask; /* gfp mask to be used for allocations */ > - pgoff_t pgoff; /* Logical page offset based on vma */ > - unsigned long address; /* Faulting virtual address */ > + struct { > + struct vm_area_struct *vma; /* Target VMA */ > + gfp_t gfp_mask; /* gfp mask to be used for allocations */ > + pgoff_t pgoff; /* Logical page offset based on vma */ > + unsigned long address; /* Faulting virtual address */ > + }; > + unsigned int flags; /* FAULT_FLAG_xxx flags > + * XXX: should really be 'const' */ > pmd_t *pmd; /* Pointer to pmd entry matching > * the 'address' */ > pud_t *pud; /* Pointer to pud entry matching > -- > 2.30.0.284.gd98b1dd5eaa7-goog >
On Wed, Jan 20, 2021 at 10:13:37AM -0800, Nick Desaulniers wrote: > On Wed, Jan 20, 2021 at 9:36 AM Will Deacon <will@kernel.org> wrote: > > > > 'struct vm_fault' contains both information about the fault being > > serviced alongside mutable fields contributing to the state of the > > fault-handling logic. Unfortunately, the distinction between the two is > > not clear-cut, and a number of callers end up manipulating the structure > > temporarily before restoring it when returning. > > > > Try to clean this up by moving the immutable fault information into an > > anonymous struct, which will later be marked as 'const'. GCC will then > > complain (with an error) about modification of these fields after they > > have been initialised, although LLVM currently allows them without even > > a warning: > > > > https://bugs.llvm.org/show_bug.cgi?id=48755 > > I think this paragraph+link would be better on patch 8/8. Agreed, I'll move it. Will
diff --git a/include/linux/mm.h b/include/linux/mm.h index 251a2339befb..b4a5cb9bff7d 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -517,11 +517,14 @@ static inline bool fault_flag_allow_retry_first(unsigned int flags) * pgoff should be used in favour of virtual_address, if possible. */ struct vm_fault { - struct vm_area_struct *vma; /* Target VMA */ - unsigned int flags; /* FAULT_FLAG_xxx flags */ - gfp_t gfp_mask; /* gfp mask to be used for allocations */ - pgoff_t pgoff; /* Logical page offset based on vma */ - unsigned long address; /* Faulting virtual address */ + struct { + struct vm_area_struct *vma; /* Target VMA */ + gfp_t gfp_mask; /* gfp mask to be used for allocations */ + pgoff_t pgoff; /* Logical page offset based on vma */ + unsigned long address; /* Faulting virtual address */ + }; + unsigned int flags; /* FAULT_FLAG_xxx flags + * XXX: should really be 'const' */ pmd_t *pmd; /* Pointer to pmd entry matching * the 'address' */ pud_t *pud; /* Pointer to pud entry matching
'struct vm_fault' contains both information about the fault being serviced alongside mutable fields contributing to the state of the fault-handling logic. Unfortunately, the distinction between the two is not clear-cut, and a number of callers end up manipulating the structure temporarily before restoring it when returning. Try to clean this up by moving the immutable fault information into an anonymous struct, which will later be marked as 'const'. GCC will then complain (with an error) about modification of these fields after they have been initialised, although LLVM currently allows them without even a warning: https://bugs.llvm.org/show_bug.cgi?id=48755 Ideally, the 'flags' field would be part of the new structure too, but it seems as though the ->page_mkwrite() path is not ready for this yet. Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/CAHk-=whYs9XsO88iqJzN6NC=D-dp2m0oYXuOoZ=eWnvv=5OA+w@mail.gmail.com Signed-off-by: Will Deacon <will@kernel.org> --- include/linux/mm.h | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)