On 2014-09-16, Hansen, Dave wrote:
> On 09/11/2014 01:46 AM, Qiaowei Ren wrote:
>> +/*
>> + * Free the backing physical pages of bounds table 'bt_addr'.
>> + * Assume start...end is within that bounds table.
>> + */
>> +static int __must_check zap_bt_entries(struct mm_struct *mm,
>> + unsigned long bt_addr,
>> + unsigned long start, unsigned long end) {
>> + struct vm_area_struct *vma;
>> +
>> + /* Find the vma which overlaps this bounds table */
>> + vma = find_vma(mm, bt_addr);
>> + /*
>> + * The table entry comes from userspace and could be
>> + * pointing anywhere, so make sure it is at least
>> + * pointing to valid memory.
>> + */
>> + if (!vma || !(vma->vm_flags & VM_MPX) ||
>> + vma->vm_start > bt_addr ||
>> + vma->vm_end < bt_addr+MPX_BT_SIZE_BYTES)
>> + return -EINVAL;
>
> If someone did *ANYTHING* to split the VMA, this check would fail. I
> think that's a little draconian, considering that somebody could do a
> NUMA policy on part of a VM_MPX VMA and cause it to be split.
>
> This check should look across the entire 'bt_addr ->
> bt_addr+MPX_BT_SIZE_BYTES' range, find all of the VM_MPX VMAs, and zap
> only those.
>
> If we encounter a non-VM_MPX vma, it should be ignored.
>
Ok.
>> + if (ret == -EFAULT)
>> + return ret;
>> +
>> + /*
>> + * unmap those bounds table which are entirely covered in this
>> + * virtual address region.
>> + */
>
> Entirely covered *AND* not at the edges, right?
>
Yes.
>> + bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
>> + bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
>> + for (bd_entry = bde_start + 1; bd_entry < bde_end; bd_entry++) {
>
> This needs a big fat comment that it is only freeing the bounds tables that
> are 1.
> fully covered 2. not at the edges of the mapping, even if full aligned
>
> Does this get any nicer if we have unmap_side_bts() *ONLY* go after
> bounds tables that are partially owned by the region being unmapped?
>
> It seems like we really should do this:
>
> for (each bt fully owned)
> unmap_single_bt()
> if (start edge unaligned)
> free start edge
> if (end edge unaligned)
> free end edge
>
> I bet the unmap_side_bts() code gets simpler if we do that, too.
>
Maybe. I will try this.
Thanks,
Qiaowei
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