Re: [PATCH perf/core 08/22] uprobes/x86: Add mapping for optimized uprobe trampolines

Oleg Nesterov
2025-04-27T17:35:51Z

On 04/27, Oleg Nesterov wrote:
>
> On 04/21, Jiri Olsa wrote:
> >
> > +static unsigned long find_nearest_page(unsigned long vaddr)
> > +{
> > + struct vm_area_struct *vma, *prev = NULL;
> > + unsigned long prev_vm_end = PAGE_SIZE;
> > + VMA_ITERATOR(vmi, current->mm, 0);
> > +
> > + vma = vma_next(&vmi);
> > + while (vma) {
> > + if (prev)
> > + prev_vm_end = prev->vm_end;
> > + if (vma->vm_start - prev_vm_end >= PAGE_SIZE) {
> > + if (is_reachable_by_call(prev_vm_end, vaddr))
> > + return prev_vm_end;
> > + if (is_reachable_by_call(vma->vm_start - PAGE_SIZE, vaddr))
> > + return vma->vm_start - PAGE_SIZE;
> > + }
> > + prev = vma;
> > + vma = vma_next(&vmi);
> > + }
> > +
> > + return 0;
> > +}
>
> This can be simplified afaics... We don't really need prev, and we can
> use for_each_vma(),
>
> static unsigned long find_nearest_page(unsigned long vaddr)
> {
> struct vm_area_struct *vma;
> unsigned long prev_vm_end = PAGE_SIZE;
> VMA_ITERATOR(vmi, current->mm, 0);
>
> for_each_vma(vmi, vma) {
> if (vma->vm_start - prev_vm_end >= PAGE_SIZE) {
> if (is_reachable_by_call(prev_vm_end, vaddr))
> return prev_vm_end;
> if (is_reachable_by_call(vma->vm_start - PAGE_SIZE, vaddr))
> return vma->vm_start - PAGE_SIZE;
> }
> prev_vm_end = vma->vm_end;
> }
>
> return 0;
> }

Either way it doesn't look nice. If nothing else, we should respect
vm_start/end_gap(vma).

Can't we do something like

struct vm_unmapped_area_info info = {};

info.length = PAGE_SIZE;
info.low_limit = vaddr - INT_MIN + 5;
info.high_limit = vaddr + INT_MAX;

info.flags = VM_UNMAPPED_AREA_TOPDOWN; // makes sense?

return vm_unmapped_area(&info);

instead ?

Oleg.