From: Dave Hansen <dave.hansen@linux.intel.com>

There are a billion ways to refer to a physical memory address.
One of the x86 PMD freeing code location chooses to use a 'pte_t *' to
point to a PMD page and then call a PTE-specific freeing function for
it.  That's a bit wonky.

Just use a 'struct ptdesc *' instead. Its entire purpose is to refer
to page table pages. It also means being able to remove an explicit
cast.

Right now, pte_free_kernel() is a one-liner that calls
pagetable_dtor_free(). Effectively, all this patch does is
remove one superfluous __pa(__va(paddr)) conversion and then
call pagetable_dtor_free() directly instead of through a helper.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
---
 include/linux/mm.h    |  6 ++++--
 arch/x86/mm/pgtable.c | 12 ++++++------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 15ce0c415d36..94e2ec6c5685 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3203,8 +3203,7 @@ 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)
-
+#if defined(CONFIG_SPLIT_PMD_PTLOCKS) || defined(CONFIG_X86_64)
 static inline struct page *pmd_pgtable_page(pmd_t *pmd)
 {
 	unsigned long mask = ~(PTRS_PER_PMD * sizeof(pmd_t) - 1);
@@ -3215,6 +3214,9 @@ static inline struct ptdesc *pmd_ptdesc(pmd_t *pmd)
 {
 	return page_ptdesc(pmd_pgtable_page(pmd));
 }
+#endif
+
+#if defined(CONFIG_SPLIT_PMD_PTLOCKS)
 
 static inline spinlock_t *pmd_lockptr(struct mm_struct *mm, pmd_t *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;
 }
-- 
2.43.0

On 14.10.25 15:04, Lu Baolu wrote:
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> There are a billion ways to refer to a physical memory address.
> One of the x86 PMD freeing code location chooses to use a 'pte_t *' to
> point to a PMD page and then call a PTE-specific freeing function for
> it.  That's a bit wonky.
> 
> Just use a 'struct ptdesc *' instead. Its entire purpose is to refer
> to page table pages. It also means being able to remove an explicit
> cast.
> 
> Right now, pte_free_kernel() is a one-liner that calls
> pagetable_dtor_free(). Effectively, all this patch does is
> remove one superfluous __pa(__va(paddr)) conversion and then
> call pagetable_dtor_free() directly instead of through a helper.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> ---
>   include/linux/mm.h    |  6 ++++--
>   arch/x86/mm/pgtable.c | 12 ++++++------
>   2 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 15ce0c415d36..94e2ec6c5685 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3203,8 +3203,7 @@ 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)
> -
> +#if defined(CONFIG_SPLIT_PMD_PTLOCKS) || defined(CONFIG_X86_64)

Yeah, that is weird. I'd have thought we can simply move this out of
the ifdef? The CONFIG_X86_64 stuff certainly has to go one way or the other.

As PTE tables always fit in a single page, pgtable_page(pte) is sufficient.

PMD tables can exceed a single page on some archs, so we have to find 
the first page first that we can then cast.

Can't immediately see why that causes compile issues.

>   static inline struct page *pmd_pgtable_page(pmd_t *pmd)
>   {
>   	unsigned long mask = ~(PTRS_PER_PMD * sizeof(pmd_t) - 1);
> @@ -3215,6 +3214,9 @@ static inline struct ptdesc *pmd_ptdesc(pmd_t *pmd)
>   {
>   	return page_ptdesc(pmd_pgtable_page(pmd));
>   }
> +#endif


-- 
Cheers

David / dhildenb