[PATCH kernel v2 2/2] powerpc/mm_iommu: Allow pinning large regions

[Alexey Kardashevskiy]

When called with vmas_arg==NULL, get_user_pages_longterm() allocates
an array of nr_pages*8 which can easily get greater that the max order,
for example, registering memory for a 256GB guest does this and fails
in __alloc_pages_nodemask().

This adds a loop over chunks of entries to fit the max order limit.

Fixes: 678e174c4c16 ("powerpc/mm/iommu: allow migration of cma allocated pages 
during mm_iommu_do_alloc", 2019-03-05)
Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
 arch/powerpc/mm/mmu_context_iommu.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/mm/mmu_context_iommu.c 
b/arch/powerpc/mm/mmu_context_iommu.c
index 9d9be850f8c2..8330f135294f 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -98,6 +98,7 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned 
long ua,
        struct mm_iommu_table_group_mem_t *mem, *mem2;
        long i, ret, locked_entries = 0, pinned = 0;
        unsigned int pageshift;
+       unsigned long entry, chunk;
 
        if (dev_hpa == MM_IOMMU_TABLE_INVALID_HPA) {
                ret = mm_iommu_adjust_locked_vm(mm, entries, true);
@@ -134,11 +135,26 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, 
unsigned long ua,
        }
 
        down_read(&mm->mmap_sem);
-       ret = get_user_pages_longterm(ua, entries, FOLL_WRITE, mem->hpages, 
NULL);
+       chunk = (1UL << (PAGE_SHIFT + MAX_ORDER - 1)) /
+                       sizeof(struct vm_area_struct *);
+       chunk = min(chunk, entries);
+       for (entry = 0; entry < entries; entry += chunk) {
+               unsigned long n = min(entries - entry, chunk);
+
+               ret = get_user_pages_longterm(ua + (entry << PAGE_SHIFT), n,
+                               FOLL_WRITE, mem->hpages + entry, NULL);
+               if (ret == n) {
+                       pinned += n;
+                       continue;
+               }
+               if (ret > 0)
+                       pinned += ret;
+               break;
+       }
        up_read(&mm->mmap_sem);
-       pinned = ret > 0 ? ret : 0;
-       if (ret != entries) {
-               ret = -EFAULT;
+       if (pinned != entries) {
+               if (!ret)
+                       ret = -EFAULT;
                goto free_exit;
        }
 
-- 
2.17.1