Re: [PATCH v4 10/15] riscv: pgtable: move pagetable_dtor() to __tlb_remove_table()

[Qi Zheng <zhengqi.arch@bytedance.com>]

Hi Kevin,

On 2025/1/3 00:53, Kevin Brodsky wrote:
> On 30/12/2024 10:07, Qi Zheng wrote:
>>   static inline void riscv_tlb_remove_ptdesc(struct mmu_gather *tlb, void *pt)
>>   {
>> -	if (riscv_use_sbi_for_rfence())
>> +	if (riscv_use_sbi_for_rfence()) {
>>   		tlb_remove_ptdesc(tlb, pt);
>> -	else
>> +	} else {
>> +		pagetable_dtor(pt);
>>   		tlb_remove_page_ptdesc(tlb, pt);
> 
> I find the imbalance pretty confusing: pagetable_dtor() is called
> explicitly before using tlb_remove_page() but not tlb_remove_ptdesc().
> Doesn't that assume that CONFIG_MMU_GATHER_HAVE_TABLE_FREE is selected?
> Could we not call pagetable_dtor() from __tlb_batch_free_encoded_pages()
> to ensure that the dtor is always called just before freeing, and remove

In __tlb_batch_free_encoded_pages(), we can indeed detect PageTable()
and call pagetable_dtor() to dtor the page table pages.
But __tlb_batch_free_encoded_pages() is also used to free normal pages
(not page table pages), so I don't want to add overhead there.

But now I think maybe we can do this in tlb_remove_page_ptdesc(), like
this:

diff --git a/arch/csky/include/asm/pgalloc.h 
b/arch/csky/include/asm/pgalloc.h
index f1ce5b7b28f22..e45c7e91dcbf9 100644
--- a/arch/csky/include/asm/pgalloc.h
+++ b/arch/csky/include/asm/pgalloc.h
@@ -63,7 +63,6 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)

  #define __pte_free_tlb(tlb, pte, address)              \
  do {                                                   \
-       pagetable_dtor(page_ptdesc(pte));               \
         tlb_remove_page_ptdesc(tlb, page_ptdesc(pte));  \
  } while (0)

diff --git a/arch/hexagon/include/asm/pgalloc.h 
b/arch/hexagon/include/asm/pgalloc.h
index 40e42a0e71673..9903449f45cff 100644
--- a/arch/hexagon/include/asm/pgalloc.h
+++ b/arch/hexagon/include/asm/pgalloc.h
@@ -89,7 +89,6 @@ static inline void pmd_populate_kernel(struct 
mm_struct *mm, pmd_t *pmd,

  #define __pte_free_tlb(tlb, pte, addr)                         \
  do {                                                           \
-       pagetable_dtor((page_ptdesc(pte)));                     \
         tlb_remove_page_ptdesc((tlb), (page_ptdesc(pte)));      \
  } while (0)

diff --git a/arch/loongarch/include/asm/pgalloc.h 
b/arch/loongarch/include/asm/pgalloc.h
index 7211dff8c969e..de5b3f5c85d1c 100644
--- a/arch/loongarch/include/asm/pgalloc.h
+++ b/arch/loongarch/include/asm/pgalloc.h
@@ -57,7 +57,6 @@ static inline pte_t *pte_alloc_one_kernel(struct 
mm_struct *mm)

  #define __pte_free_tlb(tlb, pte, address)                      \
  do {                                                           \
-       pagetable_dtor(page_ptdesc(pte));                       \
         tlb_remove_page_ptdesc((tlb), page_ptdesc(pte));        \
  } while (0)

diff --git a/arch/m68k/include/asm/sun3_pgalloc.h 
b/arch/m68k/include/asm/sun3_pgalloc.h
index 2b626cb3ad0ae..731cc8f0731d3 100644
--- a/arch/m68k/include/asm/sun3_pgalloc.h
+++ b/arch/m68k/include/asm/sun3_pgalloc.h
@@ -19,7 +19,6 @@ extern const char bad_pmd_string[];

  #define __pte_free_tlb(tlb, pte, addr)                         \
  do {                                                           \
-       pagetable_dtor(page_ptdesc(pte));                       \
         tlb_remove_page_ptdesc((tlb), page_ptdesc(pte));        \
  } while (0)

diff --git a/arch/mips/include/asm/pgalloc.h 
b/arch/mips/include/asm/pgalloc.h
index 36d9805033c4b..964ad514be281 100644
--- a/arch/mips/include/asm/pgalloc.h
+++ b/arch/mips/include/asm/pgalloc.h
@@ -56,7 +56,6 @@ static inline void pgd_free(struct mm_struct *mm, 
pgd_t *pgd)

  #define __pte_free_tlb(tlb, pte, address)                      \
  do {                                                           \
-       pagetable_dtor(page_ptdesc(pte));                       \
         tlb_remove_page_ptdesc((tlb), page_ptdesc(pte));        \
  } while (0)

diff --git a/arch/nios2/include/asm/pgalloc.h 
b/arch/nios2/include/asm/pgalloc.h
index 12a536b7bfbd4..ef6b4b8301ac6 100644
--- a/arch/nios2/include/asm/pgalloc.h
+++ b/arch/nios2/include/asm/pgalloc.h
@@ -30,7 +30,6 @@ extern pgd_t *pgd_alloc(struct mm_struct *mm);

  #define __pte_free_tlb(tlb, pte, addr)                                 \
         do {                                                            \
-               pagetable_dtor(page_ptdesc(pte));                       \
                 tlb_remove_page_ptdesc((tlb), (page_ptdesc(pte)));      \
         } while (0)

diff --git a/arch/openrisc/include/asm/pgalloc.h 
b/arch/openrisc/include/asm/pgalloc.h
index 596e2355824e3..9361205610910 100644
--- a/arch/openrisc/include/asm/pgalloc.h
+++ b/arch/openrisc/include/asm/pgalloc.h
@@ -68,7 +68,6 @@ extern pte_t *pte_alloc_one_kernel(struct mm_struct *mm);

  #define __pte_free_tlb(tlb, pte, addr)                         \
  do {                                                           \
-       pagetable_dtor(page_ptdesc(pte));                       \
         tlb_remove_page_ptdesc((tlb), (page_ptdesc(pte)));      \
  } while (0)

diff --git a/arch/riscv/include/asm/pgalloc.h 
b/arch/riscv/include/asm/pgalloc.h
index c8907b8317115..61c26576614da 100644
--- a/arch/riscv/include/asm/pgalloc.h
+++ b/arch/riscv/include/asm/pgalloc.h
@@ -25,12 +25,10 @@
   */
  static inline void riscv_tlb_remove_ptdesc(struct mmu_gather *tlb, 
void *pt)
  {
-       if (riscv_use_sbi_for_rfence()) {
+       if (riscv_use_sbi_for_rfence())
                 tlb_remove_ptdesc(tlb, pt);
-       } else {
-               pagetable_dtor(pt);
+       else
                 tlb_remove_page_ptdesc(tlb, pt);
-       }
  }

  static inline void pmd_populate_kernel(struct mm_struct *mm,
diff --git a/arch/sh/include/asm/pgalloc.h b/arch/sh/include/asm/pgalloc.h
index 96d938fdf2244..5b5c73e9fdb4b 100644
--- a/arch/sh/include/asm/pgalloc.h
+++ b/arch/sh/include/asm/pgalloc.h
@@ -34,7 +34,6 @@ static inline void pmd_populate(struct mm_struct *mm, 
pmd_t *pmd,

  #define __pte_free_tlb(tlb, pte, addr)                         \
  do {                                                           \
-       pagetable_dtor(page_ptdesc(pte));                       \
         tlb_remove_page_ptdesc((tlb), (page_ptdesc(pte)));      \
  } while (0)

diff --git a/arch/um/include/asm/pgalloc.h b/arch/um/include/asm/pgalloc.h
index f0af23c3aeb2b..4fd59fb184818 100644
--- a/arch/um/include/asm/pgalloc.h
+++ b/arch/um/include/asm/pgalloc.h
@@ -27,7 +27,6 @@ extern pgd_t *pgd_alloc(struct mm_struct *);

  #define __pte_free_tlb(tlb, pte, address)                      \
  do {                                                           \
-       pagetable_dtor(page_ptdesc(pte));                       \
         tlb_remove_page_ptdesc((tlb), (page_ptdesc(pte)));      \
  } while (0)

@@ -35,7 +34,6 @@ do { 
        \

  #define __pmd_free_tlb(tlb, pmd, address)                      \
  do {                                                           \
-       pagetable_dtor(virt_to_ptdesc(pmd));                    \
         tlb_remove_page_ptdesc((tlb), virt_to_ptdesc(pmd));     \
  } while (0)

@@ -43,7 +41,6 @@ do { 
        \

  #define __pud_free_tlb(tlb, pud, address)                      \
  do {                                                           \
-       pagetable_dtor(virt_to_ptdesc(pud));            \
         tlb_remove_page_ptdesc((tlb), virt_to_ptdesc(pud));     \
  } while (0)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index a96d4b440f3da..a59205863f431 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -506,6 +506,7 @@ static inline void tlb_remove_ptdesc(struct 
mmu_gather *tlb, void *pt)
  /* Like tlb_remove_ptdesc, but for page-like page directories. */
  static inline void tlb_remove_page_ptdesc(struct mmu_gather *tlb, 
struct ptdesc *pt)
  {
+       pagetable_dtor(pt);
         tlb_remove_page(tlb, ptdesc_page(pt));
  }

This avoids explicitly calling pagetable_dtor() in the architecture
code. If that makes sense, I can send a formal separate patch to do
this.

Thanks,
Qi


> the extra handling from arch code? I may well be missing something, I'm
> not super familiar with the tlb handling code >
> - Kevin