On 9/11/24 14:57, David Hildenbrand wrote:

On 11.09.24 08:55, Dev Jain wrote:

quoted

In preparation for the second patch, abstract away the THP allocation
logic present in the create_huge_pmd() path, which corresponds to the
faulting case when no page is present.

There should be no functional change as a result of applying
this patch.

[...]

quoted

+
+static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
+            struct vm_area_struct *vma, unsigned long haddr)
+{
+    pmd_t entry;
+
+    entry = mk_huge_pmd(&folio->page, vma->vm_page_prot);
+    entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+    folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
+    folio_add_lru_vma(folio, vma);
+    set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
+    update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);

It's quite weird to see a mixture of haddr and vmf->address, and 
likely this mixture is wrong or not not required.

Looking at arc's update_mmu_cache_pmd() implementation, I cannot see 
how passing in the unaligned address would do the right thing. But 
maybe arc also doesn't trigger that code path ... who knows :)

If I am reading correctly, arch/arc/mm/tlb.c: update_mmu_cache_pmd() 
calls update_mmu_cache_range() which is already expecting an unaligned 
address? But...

Staring at some other update_mmu_cache_pmd() users, it's quite 
inconsistent. Primarily only do_huge_pmd_numa_page() and 
__do_huge_pmd_anonymous_page() use the unaligned address. The others 
seem to use the aligned address ... as one would expect when modifying 
a PMD.

Looking at riscv: 
update_mmu_cache_pmd()->update_mmu_cache()->update_mmu_cache_range(). 
The argument getting passed to local_flush_tlb_page() seems like, should 
expect an aligned address.

I suggest to change this function to *not* pass in the vmf, and rename 
it to something like:

static void folio_map_anon_pmd(struct folio *folio, struct 
vm_area_struct *vma, pmd_t *pmd, unsigned long haddr)

Then use haddr also to do the update_mmu_cache_pmd().

quoted

+    add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+    mm_inc_nr_ptes(vma->vm_mm);
+}
+
+static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
+{
+    struct vm_area_struct *vma = vmf->vma;
+    struct folio *folio;
+    pgtable_t pgtable;
+    unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+    vm_fault_t ret = 0;
+    gfp_t gfp = vma_thp_gfp_mask(vma);

Nit: While at it, try to use reverse christmas-tree where possible, 
makes things more reasible. You could make haddr const.

struct vm_area_struct *vma = vmf->vma;
unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
gfp_t gfp = vma_thp_gfp_mask(vma);
struct folio *folio;
vm_fault_t ret = 0;
...

quoted

+
+    folio = pmd_thp_fault_alloc(gfp, vma, haddr, vmf->address);
+    if (unlikely(!folio)) {
+        ret = VM_FAULT_FALLBACK;
+        goto release;
+    }
+
+    pgtable = pte_alloc_one(vma->vm_mm);
+    if (unlikely(!pgtable)) {
+        ret = VM_FAULT_OOM;
+        goto release;
+    }
        vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+

Nit Unrelated change.

quoted

      if (unlikely(!pmd_none(*vmf->pmd))) {
          goto unlock_release;