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

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Message-ID: <20250427173456.GB27775@redhat.com>
Date: Sun, 27 Apr 2025 19:34:56 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	x86@...nel.org, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Alan Maguire <alan.maguire@...cle.com>,
	David Laight <David.Laight@...LAB.COM>,
	Thomas Weißschuh <thomas@...ch.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH perf/core 08/22] uprobes/x86: Add mapping for optimized
 uprobe trampolines

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.