linux-kernel - Re: [PATCH v5 3/8] x86/mm: Use 'ptdesc' when freeing PMD pages

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Message-ID: <ce126bc8-7672-4071-96b5-9652e736175b@linux.intel.com>
Date: Sat, 11 Oct 2025 14:26:53 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Dave Hansen <dave.hansen@...el.com>, David Hildenbrand
 <david@...hat.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Kevin Tian <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...dia.com>,
 Jann Horn <jannh@...gle.com>, Vasant Hegde <vasant.hegde@....com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Alistair Popple <apopple@...dia.com>,
 Peter Zijlstra <peterz@...radead.org>, Uladzislau Rezki <urezki@...il.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Andy Lutomirski <luto@...nel.org>, Yi Lai <yi1.lai@...el.com>
Cc: iommu@...ts.linux.dev, security@...nel.org, x86@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v5 3/8] x86/mm: Use 'ptdesc' when freeing PMD pages

On 10/10/25 03:31, Dave Hansen wrote:
> On 10/9/25 12:25, David Hildenbrand wrote:
>>>
>>> @@ -750,8 +750,8 @@ int pud_free_pmd_page(pud_t *pud, unsigned long addr)
>>>          for (i = 0; i < PTRS_PER_PMD; i++) {
>>>            if (!pmd_none(pmd_sv[i])) {
>>> -            pte = (pte_t *)pmd_page_vaddr(pmd_sv[i]);
>>> -            pte_free_kernel(&init_mm, pte);
>>> +            pt = page_ptdesc(pmd_page(pmd_sv[i]));
>>> +            pagetable_dtor_free(pt);
>>
>> There is pmd_ptdesc() which does
>>
>>      page_ptdesc(pmd_pgtable_page(pmd));
>>
>> It's buried in a
>>
>>      #if defined(CONFIG_SPLIT_PMD_PTLOCKS)
>>
>> Can't we just make that always available so we can use it here?
> 
> Yes, that looks like a good idea. I never noticed pmd_ptdesc() when I
> was writing this for sure.

I updated the patch like this,

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6a0bb7fc3148..a0850dc6878e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3203,8 +3203,6 @@ pte_t *pte_offset_map_rw_nolock(struct mm_struct 
*mm, pmd_t *pmd,
         ((unlikely(pmd_none(*(pmd))) && __pte_alloc_kernel(pmd))? \
                 NULL: pte_offset_kernel(pmd, address))

-#if defined(CONFIG_SPLIT_PMD_PTLOCKS)
-
  static inline struct page *pmd_pgtable_page(pmd_t *pmd)
  {
         unsigned long mask = ~(PTRS_PER_PMD * sizeof(pmd_t) - 1);
@@ -3216,6 +3214,8 @@ static inline struct ptdesc *pmd_ptdesc(pmd_t *pmd)
         return page_ptdesc(pmd_pgtable_page(pmd));
  }

+#if defined(CONFIG_SPLIT_PMD_PTLOCKS)
+
  static inline spinlock_t *pmd_lockptr(struct mm_struct *mm, pmd_t *pmd)
  {
         return ptlock_ptr(pmd_ptdesc(pmd));
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index ddf248c3ee7d..c830ccbc2fd8 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -729,7 +729,7 @@ int pmd_clear_huge(pmd_t *pmd)
  int pud_free_pmd_page(pud_t *pud, unsigned long addr)
  {
         pmd_t *pmd, *pmd_sv;
-       pte_t *pte;
+       struct ptdesc *pt;
         int i;

         pmd = pud_pgtable(*pud);
@@ -750,8 +750,8 @@ int pud_free_pmd_page(pud_t *pud, unsigned long addr)

         for (i = 0; i < PTRS_PER_PMD; i++) {
                 if (!pmd_none(pmd_sv[i])) {
-                       pte = (pte_t *)pmd_page_vaddr(pmd_sv[i]);
-                       pte_free_kernel(&init_mm, pte);
+                       pt = pmd_ptdesc(&pmd_sv[i]);
+                       pagetable_dtor_free(pt);
                 }
         }

@@ -772,15 +772,15 @@ int pud_free_pmd_page(pud_t *pud, unsigned long addr)
   */
  int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
  {
-       pte_t *pte;
+       struct ptdesc *pt;

-       pte = (pte_t *)pmd_page_vaddr(*pmd);
+       pt = pmd_ptdesc(pmd);
         pmd_clear(pmd);

         /* INVLPG to clear all paging-structure caches */
         flush_tlb_kernel_range(addr, addr + PAGE_SIZE-1);

-       pte_free_kernel(&init_mm, pte);
+       pagetable_dtor_free(pt);

         return 1;
  }

Thanks,
baolu