2022-04-01 16:14:56

by Chuanhua Han

Subject: [PATCH v4] riscv: mm: Remove the copy operation of pmd

Since all processes share the kernel address space,
we only need to copy pgd in case of a vmalloc page
fault exception, the other levels of page tables are
shared, so the operation of copying pmd is unnecessary.

Signed-off-by: Chuanhua Han <[email protected]>
---
Changes in v4:
-Modify incorrect author name.

Changes in v3:
-Change the real name of signed-off-by.

Changes in v2:
-Delete incorrect default signatures.


arch/riscv/mm/fault.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 4e9efbe46d5f..40694f0cab9e 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -102,9 +102,9 @@ static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code
static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
{
pgd_t *pgd, *pgd_k;
- pud_t *pud, *pud_k;
- p4d_t *p4d, *p4d_k;
- pmd_t *pmd, *pmd_k;
+ pud_t *pud_k;
+ p4d_t *p4d_k;
+ pmd_t *pmd_k;
pte_t *pte_k;
int index;
unsigned long pfn;
@@ -132,14 +132,12 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
}
set_pgd(pgd, *pgd_k);

- p4d = p4d_offset(pgd, addr);
p4d_k = p4d_offset(pgd_k, addr);
if (!p4d_present(*p4d_k)) {
no_context(regs, addr);
return;
}

- pud = pud_offset(p4d, addr);
pud_k = pud_offset(p4d_k, addr);
if (!pud_present(*pud_k)) {
no_context(regs, addr);
@@ -150,13 +148,11 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
* Since the vmalloc area is global, it is unnecessary
* to copy individual PTEs
*/
- pmd = pmd_offset(pud, addr);
pmd_k = pmd_offset(pud_k, addr);
if (!pmd_present(*pmd_k)) {
no_context(regs, addr);
return;
}
- set_pmd(pmd, *pmd_k);

/*
* Make sure the actual PTE exists as well to
--
2.25.1

2022-04-22 17:58:33

by Palmer Dabbelt

Subject: Re: [PATCH v4] riscv: mm: Remove the copy operation of pmd

On Thu, 31 Mar 2022 19:43:20 PDT (-0700), [email protected] wrote:
> Since all processes share the kernel address space,
> we only need to copy pgd in case of a vmalloc page
> fault exception, the other levels of page tables are
> shared, so the operation of copying pmd is unnecessary.
>
> Signed-off-by: Chuanhua Han <[email protected]>
> ---
> Changes in v4:
> -Modify incorrect author name.
>
> Changes in v3:
> -Change the real name of signed-off-by.
>
> Changes in v2:
> -Delete incorrect default signatures.
>
>
> arch/riscv/mm/fault.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 4e9efbe46d5f..40694f0cab9e 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -102,9 +102,9 @@ static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code
> static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
> {
> pgd_t *pgd, *pgd_k;
> - pud_t *pud, *pud_k;
> - p4d_t *p4d, *p4d_k;
> - pmd_t *pmd, *pmd_k;
> + pud_t *pud_k;
> + p4d_t *p4d_k;
> + pmd_t *pmd_k;
> pte_t *pte_k;
> int index;
> unsigned long pfn;
> @@ -132,14 +132,12 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
> }
> set_pgd(pgd, *pgd_k);
>
> - p4d = p4d_offset(pgd, addr);
> p4d_k = p4d_offset(pgd_k, addr);
> if (!p4d_present(*p4d_k)) {
> no_context(regs, addr);
> return;
> }
>
> - pud = pud_offset(p4d, addr);
> pud_k = pud_offset(p4d_k, addr);
> if (!pud_present(*pud_k)) {
> no_context(regs, addr);
> @@ -150,13 +148,11 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
> * Since the vmalloc area is global, it is unnecessary
> * to copy individual PTEs
> */
> - pmd = pmd_offset(pud, addr);
> pmd_k = pmd_offset(pud_k, addr);
> if (!pmd_present(*pmd_k)) {
> no_context(regs, addr);
> return;
> }
> - set_pmd(pmd, *pmd_k);
>
> /*
> * Make sure the actual PTE exists as well to

Thanks, this is on for-next (it was last night, but looks like I forgot
to send the email).