On 08.09.2021 09:36, Juergen Gross wrote:
Commit 0881ace292b662 ("mm/mremap: use pmd/pud_poplulate to update page table entries") introduced a regression when running as Xen PV guest.
The description of that change starts with "pmd/pud_populate is the right interface to be used to set the respective page table entries." If this is deemed true, I don't think pmd_populate() should call paravirt_alloc_pte(): The latter function, as its name says, is supposed to be called for newly allocated page tables only (aiui).
Today pmd/pud_poplulate() for Xen PV assumes that the PFN inserted is referencing a not yet used page table. In case of move_normal_pmd/pud() this is not true, resulting in WARN splats like:
I agree for the PMD part, but is including PUD here really correct? While I don't know why that is, xen_alloc_ptpage() pins L1 tables only. Hence a PUD update shouldn't be able to find a pinned L2 table.
Jan