On 11.09.24 15:05, Dev Jain wrote:

On 9/11/24 18:30, David Hildenbrand wrote:

quoted

On 11.09.24 14:53, Dev Jain wrote:

quoted

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

quoted

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...

So update_mmu_cache_pmd() calls

     update_mmu_cache_range(NULL, vma, addr, &pte, HPAGE_PMD_NR);

But update_mmu_cache_range() only aligns it *to page boundary*:

     unsigned long vaddr = vaddr_unaligned & PAGE_MASK;

Ah, totally missed that it was PAGE_MASK. Thanks.

quoted

We obtain the correct hugepage-aligned physical address from the PTE

     phys_addr_t paddr = pte_val(*ptep) & PAGE_MASK_PHYS;

Then, we look at the offset in our folio

     unsigned long offset = offset_in_folio(folio, paddr);

And adjust both vaddr and paddr

     paddr -= offset;
     vaddr -= offset;

To then use that combination with

     __inv_icache_pages(paddr, vaddr, nr);

If I am not wrong, getting a non-hugepage aligned vaddr messes up
things here. But only regarding the icache I think.

Looks like it...

As we are adding a fresh page where there previously wasn't anything 
mapped (no icache invaldiation required?), and because most anon 
mappings are not executable, maybe that's why nobody notices so far.

-- 
Cheers,

David / dhildenb