Re: [PATCH v2] mm/hugetlb: fix hugetlb vs. core-mm PT locking

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 30.07.24 23:17, James Houghton wrote:
On Tue, Jul 30, 2024 at 2:07 PM David Hildenbrand <david@xxxxxxxxxx> wrote:

On 30.07.24 23:00, David Hildenbrand wrote:
On 30.07.24 22:43, James Houghton wrote:
On Tue, Jul 30, 2024 at 1:03 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b100df8cb5857..1b1f40ff00b7d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2926,6 +2926,12 @@ static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd)
           return ptlock_ptr(page_ptdesc(pmd_page(*pmd)));
    }

+static inline spinlock_t *ptep_lockptr(struct mm_struct *mm, pte_t *pte)
+{
+       BUILD_BUG_ON(IS_ENABLED(CONFIG_HIGHPTE));
+       return ptlock_ptr(virt_to_ptdesc(pte));

Hi David,


Hi!

Small question: ptep_lockptr() does not handle the case where the size
of the PTE table is larger than PAGE_SIZE, but pmd_lockptr() does.

I thought I convinced myself that leaf page tables are always single
pages and had a comment in v1.

But now I have to double-check again, and staring at
pagetable_pte_ctor() callers I am left confused.

It certainly sounds more future proof to just align the pointer down to
the start of the PTE table like pmd_lockptr() would.

IIUC, for pte_lockptr() and ptep_lockptr() to return the same result
in this case, ptep_lockptr() should be doing the masking that
pmd_lockptr() is doing. Are you sure that you don't need to be doing
it? (Or maybe I am misunderstanding something.)

It's a valid concern even if it would not be required. But I'm afraid I
won't dig into the details and simply do the alignment in a v3.

To be precise, the following on top:

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1b1f40ff00b7d..f6c7fe8f5746f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2926,10 +2926,22 @@ static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd)
          return ptlock_ptr(page_ptdesc(pmd_page(*pmd)));
   }

-static inline spinlock_t *ptep_lockptr(struct mm_struct *mm, pte_t *pte)
+static inline struct page *ptep_pgtable_page(pte_t *pte)
   {
+       unsigned long mask = ~(PTRS_PER_PTE * sizeof(pte_t) - 1);
+
          BUILD_BUG_ON(IS_ENABLED(CONFIG_HIGHPTE));
-       return ptlock_ptr(virt_to_ptdesc(pte));
+       return virt_to_page((void *)((unsigned long)pte & mask));
+}
+
+static inline struct ptdesc *ptep_ptdesc(pte_t *pte)
+{
+       return page_ptdesc(ptep_pgtable_page(pte));
+}
+
+static inline spinlock_t *ptep_lockptr(struct mm_struct *mm, pte_t *pte)
+{
+       return ptlock_ptr(ptep_ptdesc(pte));
   }

Thanks! That looks right to me. Feel free to add

Reviewed-by: James Houghton <jthoughton@xxxxxxxxxx>

Thanks for the review, will send a v3 tomorrow after having wasted more valuable life time setting up the ARM environment again ... :)

--
Cheers,

David / dhildenb





[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux