From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> Subject: powerpc/mm/iommu: allow large IOMMU page size only for hugetlb backing THP pages can get split during different code paths. An incremented reference count does imply we will not split the compound page. But the pmd entry can be converted to level 4 pte entries. Keep the code simpler by allowing large IOMMU page size only if the guest ram is backed by hugetlb pages. Link: http://lkml.kernel.org/r/20190114095438.32470-6-aneesh.kumar@xxxxxxxxxxxxx Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Cc: Alexey Kardashevskiy <aik@xxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/powerpc/mm/mmu_context_iommu.c | 22 ++++++---------------- 1 file changed, 6 insertions(+), 16 deletions(-) --- a/arch/powerpc/mm/mmu_context_iommu.c~powerpc-mm-iommu-allow-large-iommu-page-size-only-for-hugetlb-backing +++ a/arch/powerpc/mm/mmu_context_iommu.c @@ -98,8 +98,6 @@ static long mm_iommu_do_alloc(struct mm_ struct mm_iommu_table_group_mem_t *mem; long i, ret, locked_entries = 0; unsigned int pageshift; - unsigned long flags; - unsigned long cur_ua; mutex_lock(&mem_list_mutex); @@ -167,22 +165,14 @@ static long mm_iommu_do_alloc(struct mm_ for (i = 0; i < entries; ++i) { struct page *page = mem->hpages[i]; - cur_ua = ua + (i << PAGE_SHIFT); - if (mem->pageshift > PAGE_SHIFT && PageCompound(page)) { - pte_t *pte; + /* + * Allow to use larger than 64k IOMMU pages. Only do that + * if we are backed by hugetlb. + */ + if ((mem->pageshift > PAGE_SHIFT) && PageHuge(page)) { struct page *head = compound_head(page); - unsigned int compshift = compound_order(head); - unsigned int pteshift; - - local_irq_save(flags); /* disables as well */ - pte = find_linux_pte(mm->pgd, cur_ua, NULL, &pteshift); - /* Double check it is still the same pinned page */ - if (pte && pte_page(*pte) == head && - pteshift == compshift + PAGE_SHIFT) - pageshift = max_t(unsigned int, pteshift, - PAGE_SHIFT); - local_irq_restore(flags); + pageshift = compound_order(head) + PAGE_SHIFT; } mem->pageshift = min(mem->pageshift, pageshift); /* _
