Re: [PATCH 1/4 v2] LoongArch: mm: Add page table mapped mode support

[Huacai Chen <chenhuacai@kernel.org>]

Hi, Enze,

On Tue, Jul 25, 2023 at 2:15 PM Enze Li <lienze@kylinos.cn> wrote:
>
> According to LoongArch documentation online, there are two types of address
> translation modes: direct mapped address translation mode (direct mapped mode)
> and page table mapped address translation mode (page table mapped mode).
>
> Currently, the upstream kernel only supports direct mapped mode.
> This patch adds a function that determines whether page table mapped
> mode should be used, and also adds the corresponding handler functions
> for both modes.
>
> For more details on the two modes, see [1].
>
> [1] https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#virtual-address-space-and-address-translation-mode
>
> Signed-off-by: Enze Li <lienze@kylinos.cn>
> ---
>  arch/loongarch/include/asm/page.h    | 19 ++++++++++++++++++-
>  arch/loongarch/include/asm/pgtable.h |  2 ++
>  arch/loongarch/mm/pgtable.c          |  6 ++++++
>  3 files changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/include/asm/page.h b/arch/loongarch/include/asm/page.h
> index 26e8dccb6619..e43a2385b2cd 100644
> --- a/arch/loongarch/include/asm/page.h
> +++ b/arch/loongarch/include/asm/page.h
> @@ -32,6 +32,7 @@
>
>  #include <linux/kernel.h>
>  #include <linux/pfn.h>
> +#include <asm/cpu-features.h>
>
>  /*
>   * It's normally defined only for FLATMEM config but it's
> @@ -84,7 +85,23 @@ typedef struct { unsigned long pgprot; } pgprot_t;
>  #define sym_to_pfn(x)          __phys_to_pfn(__pa_symbol(x))
>
>  #define virt_to_pfn(kaddr)     PFN_DOWN(PHYSADDR(kaddr))
> -#define virt_to_page(kaddr)    pfn_to_page(virt_to_pfn(kaddr))
> +
> +static inline bool is_tlb_addr(unsigned long kaddr)
> +{
> +       if (unlikely((kaddr & GENMASK(BITS_PER_LONG - 1, cpu_vabits)) ==
> +                    GENMASK(BITS_PER_LONG - 1, cpu_vabits)))
> +               return true;
> +       return false;
I think this helper can simply "return (kaddr >= vm_map_base)"? If so,
we can even remove this helper and use the simple condition in
virt_to_page().

> +}
> +
> +#define dwm_virt_to_page(kaddr)        pfn_to_page(virt_to_pfn(kaddr))
This should be "dmw", not "dwm", and since tlb_virt_to_page is in .c
file, this one should also be there.

Huacai
> +
> +#define virt_to_page(kaddr)                                            \
> +({                                                                     \
> +       is_tlb_addr((unsigned long)kaddr) ?                             \
> +       tlb_virt_to_page((unsigned long)kaddr) :                        \
> +       dwm_virt_to_page((unsigned long)kaddr);                         \
> +})
>
>  extern int __virt_addr_valid(volatile void *kaddr);
>  #define virt_addr_valid(kaddr) __virt_addr_valid((volatile void *)(kaddr))
> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> index 38afeb7dd58b..98a0c98de9d1 100644
> --- a/arch/loongarch/include/asm/pgtable.h
> +++ b/arch/loongarch/include/asm/pgtable.h
> @@ -353,6 +353,8 @@ static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *pt
>  #define PMD_T_LOG2     (__builtin_ffs(sizeof(pmd_t)) - 1)
>  #define PTE_T_LOG2     (__builtin_ffs(sizeof(pte_t)) - 1)
>
> +inline struct page *tlb_virt_to_page(unsigned long kaddr);
> +
>  extern pgd_t swapper_pg_dir[];
>  extern pgd_t invalid_pg_dir[];
>
> diff --git a/arch/loongarch/mm/pgtable.c b/arch/loongarch/mm/pgtable.c
> index 36a6dc0148ae..20e7425d235d 100644
> --- a/arch/loongarch/mm/pgtable.c
> +++ b/arch/loongarch/mm/pgtable.c
> @@ -9,6 +9,12 @@
>  #include <asm/pgtable.h>
>  #include <asm/tlbflush.h>
>
> +inline struct page *tlb_virt_to_page(unsigned long kaddr)
> +{
> +       return pte_page(*virt_to_kpte(kaddr));
> +}
> +EXPORT_SYMBOL_GPL(tlb_virt_to_page);
> +
>  pgd_t *pgd_alloc(struct mm_struct *mm)
>  {
>         pgd_t *ret, *init;
> --
> 2.34.1
>
>