[PATCH 1/4] riscv: tlb: fix __p*d_free_tlb()
Alexandre Ghiti
alex at ghiti.fr
Sat Dec 30 22:21:38 PST 2023
Hi Jisheng,
On 19/12/2023 18:50, Jisheng Zhang wrote:
> If non-leaf PTEs I.E pmd, pud or p4d is modified, a sfence.vma is
> a must for safe, imagine if an implementation caches the non-leaf
> translation in TLB, although I didn't meet this HW so far, but it's
> possible in theory.
>
> Signed-off-by: Jisheng Zhang<jszhang at kernel.org>
> ---
> arch/riscv/include/asm/pgalloc.h | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/pgalloc.h b/arch/riscv/include/asm/pgalloc.h
> index d169a4f41a2e..a12fb83fa1f5 100644
> --- a/arch/riscv/include/asm/pgalloc.h
> +++ b/arch/riscv/include/asm/pgalloc.h
> @@ -95,7 +95,13 @@ static inline void pud_free(struct mm_struct *mm, pud_t *pud)
> __pud_free(mm, pud);
> }
>
> -#define __pud_free_tlb(tlb, pud, addr) pud_free((tlb)->mm, pud)
> +#define __pud_free_tlb(tlb, pud, addr) \
> +do { \
> + if (pgtable_l4_enabled) { \
> + pagetable_pud_dtor(virt_to_ptdesc(pud)); \
> + tlb_remove_page_ptdesc((tlb), virt_to_ptdesc(pud)); \
The specification indeed states that an sfence.vma must be emitted after
a page directory modification. Your change is not enough though since
eventually tlb_flush() is called and in this function we should add:
if (tlb->freed_tables)
tlb_flush_mm();
otherwise we are not guaranteed that a "global" sfence.vma is called.
Would you be able to benchmark this change and see the performance impact?
Thanks,
Alex
> + } \
> +} while (0)
>
> #define p4d_alloc_one p4d_alloc_one
> static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr)
> @@ -124,7 +130,11 @@ static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
> __p4d_free(mm, p4d);
> }
>
> -#define __p4d_free_tlb(tlb, p4d, addr) p4d_free((tlb)->mm, p4d)
> +#define __p4d_free_tlb(tlb, p4d, addr) \
> +do { \
> + if (pgtable_l5_enabled) \
> + tlb_remove_page_ptdesc((tlb), virt_to_ptdesc(p4d)); \
> +} while (0)
> #endif /* __PAGETABLE_PMD_FOLDED */
>
> static inline void sync_kernel_mappings(pgd_t *pgd)
> @@ -149,7 +159,11 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
>
> #ifndef __PAGETABLE_PMD_FOLDED
>
> -#define __pmd_free_tlb(tlb, pmd, addr) pmd_free((tlb)->mm, pmd)
> +#define __pmd_free_tlb(tlb, pmd, addr) \
> +do { \
> + pagetable_pmd_dtor(virt_to_ptdesc(pmd)); \
> + tlb_remove_page_ptdesc((tlb), virt_to_ptdesc(pmd)); \
> +} while (0)
>
> #endif /* __PAGETABLE_PMD_FOLDED */
>
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