Re: [PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground pagereplacement.

[Oleg Nesterov]

On 06/07, Srikar Dronamraju wrote:
>
> +static int __replace_page(struct vm_area_struct *vma, struct page *page,
> +					struct page *kpage)
> +{
> +	struct mm_struct *mm = vma->vm_mm;
> +	pgd_t *pgd;
> +	pud_t *pud;
> +	pmd_t *pmd;
> +	pte_t *ptep;
> +	spinlock_t *ptl;
> +	unsigned long addr;
> +	int err = -EFAULT;
> +
> +	addr = page_address_in_vma(page, vma);
> +	if (addr == -EFAULT)
> +		goto out;
> +
> +	pgd = pgd_offset(mm, addr);
> +	if (!pgd_present(*pgd))
> +		goto out;
> +
> +	pud = pud_offset(pgd, addr);
> +	if (!pud_present(*pud))
> +		goto out;
> +
> +	pmd = pmd_offset(pud, addr);
> +	if (pmd_trans_huge(*pmd) || (!pmd_present(*pmd)))
> +		goto out;

Hmm. So it doesn't work with transhuge pages? May be the caller should
use __gup(FOLL_SPLIT), otherwise set_bkpt/etc can fail "mysteriously", no?
OTOH, I don't really understand how pmd_trans_huge() is possible, valid_vma()
checks ->vm_file != NULL and I iiuc transparent hugepages can only work
with anonymous mappings. Confused...

But the real problem (afaics) is VM_HUGETLB mappings. I can't understand
how __replace_page() can work in this case. Probably valid_vma() should
fail if is_vm_hugetlb_page()?

Oleg.

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