Re: [PATCH rfc -next 01/10] mm: add a generic VMA lock-based page fault handler

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On 2023/7/14 9:52, Kefeng Wang wrote:


On 2023/7/14 4:12, Suren Baghdasaryan wrote:
On Thu, Jul 13, 2023 at 9:15 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:

+int try_vma_locked_page_fault(struct vm_locked_fault *vmlf, vm_fault_t *ret)
+{
+     struct vm_area_struct *vma;
+     vm_fault_t fault;


On Thu, Jul 13, 2023 at 05:53:29PM +0800, Kefeng Wang wrote:
+#define VM_LOCKED_FAULT_INIT(_name, _mm, _address, _fault_flags, _vm_flags, _regs, _fault_code) \
+     _name.mm                = _mm;                  \
+     _name.address           = _address;             \
+     _name.fault_flags       = _fault_flags;         \
+     _name.vm_flags          = _vm_flags;            \
+     _name.regs              = _regs;                \
+     _name.fault_code        = _fault_code

More consolidated code is a good idea; no question.  But I don't think
this is the right way to do it.

I agree it is not good enough, but the arch's vma check acess has
different implementation, some use vm flags, some need fault code and
regs, and some use both :(


+int __weak arch_vma_check_access(struct vm_area_struct *vma,
+                              struct vm_locked_fault *vmlf);

This should be:

#ifndef vma_check_access
bool vma_check_access(struct vm_area_struct *vma, )
{
         return (vma->vm_flags & vm_flags) == 0;
}
#endif

and then arches which want to do something different can just define
vma_check_access.

Ok, I could convert to use this way.


+int try_vma_locked_page_fault(struct vm_locked_fault *vmlf, vm_fault_t *ret)
+{
+     struct vm_area_struct *vma;
+     vm_fault_t fault;

Declaring the vmf in this function and then copying it back is just wrong.
We need to declare vm_fault_t earlier (in the arch fault handler) and
pass it in.

Actually I passed the vm_fault_t *ret(in the arch fault handler), we
could directly use *ret instead of a new local variable, and no copy.

Did you mean to say "we need to declare vmf (struct vm_fault) earlier
(in the arch fault handler) and pass it in." ?

After recheck the code, I think Matthew' idea is 'declare vmf (struct vm_fault) earlier' like Suren said, not vm_fault_t, right? will try this, thanks.


  I don't think that creating struct vm_locked_fault is the
right idea either.

As mentioned above for vma check access, we need many arguments for a function, a new struct looks possible better, is there better solution
or any suggestion?

Thanks.





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