On 11.09.24 15:05, Dev Jain wrote:
On 9/11/24 18:30, David Hildenbrand wrote:
On 11.09.24 14:53, Dev Jain wrote:
On 9/11/24 14:57, David Hildenbrand wrote:
On 11.09.24 08:55, Dev Jain wrote:
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.
[...]
+
+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.
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
