Re: [External] Re: [PATCH v2] fs/proc/kcore.c: add mmap interface

[zhoufeng]

在 2021/6/2 上午10:22, Andrew Morton 写道:
> On Tue,  1 Jun 2021 16:22:41 +0800 Feng zhou <zhoufeng.zf@xxxxxxxxxxxxx> wrote:
>
> > From: ZHOUFENG <zhoufeng.zf@xxxxxxxxxxxxx>
> >
> > When we do the kernel monitor, use the DRGN
> > (https://github.com/osandov/drgn) access to kernel data structures,
> > found that the system calls a lot. DRGN is implemented by reading
> > /proc/kcore. After looking at the kcore code, it is found that kcore
> > does not implement mmap, resulting in frequent context switching
> > triggered by read. Therefore, we want to add mmap interface to optimize
> > performance. Since vmalloc and module areas will change with allocation
> > and release, consistency cannot be guaranteed, so mmap interface only
> > maps KCORE_TEXT and KCORE_RAM.
> >
> > ...
> >
> > +static int mmap_kcore(struct file *file, struct vm_area_struct *vma)
> > +{
> > +	size_t size = vma->vm_end - vma->vm_start;
> > +	u64 start, pfn;
> > +	int nphdr;
> > +	size_t data_offset;
> > +	size_t phdrs_len, notes_len;
> > +	struct kcore_list *m = NULL;
> > +	int ret = 0;
> > +
> > +	down_read(&kclist_lock);
> > +
> > +	get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
> > +
> > +	start = kc_offset_to_vaddr(((u64)vma->vm_pgoff << PAGE_SHIFT) -
> > +		((data_offset >> PAGE_SHIFT) << PAGE_SHIFT));
> > +
> > +	list_for_each_entry(m, &kclist_head, list) {
> > +		if (start >= m->addr && size <= m->size)
> > +			break;
> > +	}
> > +
> > +	if (&m->list == &kclist_head) {
> > +		ret = -EINVAL;
> > +		goto out;
> > +	}
> > +
> > +	if (vma->vm_flags & (VM_WRITE | VM_EXEC)) {
> > +		ret = -EPERM;
> > +		goto out;
> > +	}
> > +
> > +	vma->vm_flags &= ~(VM_MAYWRITE | VM_MAYEXEC);
> > +	vma->vm_flags |= VM_MIXEDMAP;
> > +	vma->vm_ops = &kcore_mmap_ops;
> > +
> > +	if (kern_addr_valid(start)) {
> > +		if (m->type == KCORE_RAM || m->type == KCORE_REMAP)
>
> KCORE_REMAP was removed by
> https://lkml.kernel.org/r/20210526093041.8800-2-david@xxxxxxxxxx
>
> I did this:
>
> --- a/fs/proc/kcore.c~fs-proc-kcorec-add-mmap-interface-fix
> +++ a/fs/proc/kcore.c
> @@ -660,7 +660,7 @@ static int mmap_kcore(struct file *file,
>   	vma->vm_ops = &kcore_mmap_ops;
>   
>   	if (kern_addr_valid(start)) {
> -		if (m->type == KCORE_RAM || m->type == KCORE_REMAP)
> +		if (m->type == KCORE_RAM)
>   			pfn = __pa(start) >> PAGE_SHIFT;
>   		else if (m->type == KCORE_TEXT)
>   			pfn = __pa_symbol(start) >> PAGE_SHIFT;

  Thank you very much.