Re: [PATCH v2 1/3] LoongArch: Set initial pte entry with PAGE_GLOBAL for kernel space

[Huacai Chen <chenhuacai@kernel.org>]

On Fri, Oct 18, 2024 at 11:44 AM maobibo <maobibo@loongson.cn> wrote:
>
>
>
> On 2024/10/18 上午11:14, Huacai Chen wrote:
> > Hi, Bibo,
> >
> > I applied this patch but drop the part of arch/loongarch/mm/kasan_init.c:
> > https://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson.git/commit/?h=loongarch-next&id=15832255e84494853f543b4c70ced50afc403067
> >
> > Because kernel_pte_init() should operate on page-table pages, not on
> > data pages. You have already handle page-table page in
> > mm/kasan/init.c, and if we don't drop the modification on data pages
> > in arch/loongarch/mm/kasan_init.c, the kernel fail to boot if KASAN is
> > enabled.
> >
> static inline void set_pte(pte_t *ptep, pte_t pteval)
>   {
>         WRITE_ONCE(*ptep, pteval);
> -
> -       if (pte_val(pteval) & _PAGE_GLOBAL) {
> -               pte_t *buddy = ptep_buddy(ptep);
> -               /*
> -                * Make sure the buddy is global too (if it's !none,
> -                * it better already be global)
> -                */
> -               if (pte_none(ptep_get(buddy))) {
> -#ifdef CONFIG_SMP
> -                       /*
> -                        * For SMP, multiple CPUs can race, so we need
> -                        * to do this atomically.
> -                        */
> -                       __asm__ __volatile__(
> -                       __AMOR "$zero, %[global], %[buddy] \n"
> -                       : [buddy] "+ZB" (buddy->pte)
> -                       : [global] "r" (_PAGE_GLOBAL)
> -                       : "memory");
> -
> -                       DBAR(0b11000); /* o_wrw = 0b11000 */
> -#else /* !CONFIG_SMP */
> -                       WRITE_ONCE(*buddy, __pte(pte_val(ptep_get(buddy)) | _PAGE_GLOBAL));
> -#endif /* CONFIG_SMP */
> -               }
> -       }
> +       DBAR(0b11000); /* o_wrw = 0b11000 */
>   }
>
> No, please hold on. This issue exists about twenty years, Do we need be
> in such a hurry now?
>
> why is DBAR(0b11000) added in set_pte()?
It exists before, not added by this patch. The reason is explained in
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.12-rc3&id=f93f67d06b1023313ef1662eac490e29c025c030

Huacai

>
> Regards
> Bibo Mao
> > Huacai
> >
> > On Mon, Oct 14, 2024 at 11:59 AM Bibo Mao <maobibo@loongson.cn> wrote:
> >>
> >> Unlike general architectures, there are two pages in one TLB entry
> >> on LoongArch system. For kernel space, it requires both two pte
> >> entries with PAGE_GLOBAL bit set, else HW treats it as non-global
> >> tlb, there will be potential problems if tlb entry for kernel space
> >> is not global. Such as fail to flush kernel tlb with function
> >> local_flush_tlb_kernel_range() which only flush tlb with global bit.
> >>
> >> With function kernel_pte_init() added, it can be used to init pte
> >> table when it is created for kernel address space, and the default
> >> initial pte value is PAGE_GLOBAL rather than zero at beginning.
> >>
> >> Kernel address space areas includes fixmap, percpu, vmalloc, kasan
> >> and vmemmap areas set default pte entry with PAGE_GLOBAL set.
> >>
> >> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> >> ---
> >>   arch/loongarch/include/asm/pgalloc.h | 13 +++++++++++++
> >>   arch/loongarch/include/asm/pgtable.h |  1 +
> >>   arch/loongarch/mm/init.c             |  4 +++-
> >>   arch/loongarch/mm/kasan_init.c       |  4 +++-
> >>   arch/loongarch/mm/pgtable.c          | 22 ++++++++++++++++++++++
> >>   include/linux/mm.h                   |  1 +
> >>   mm/kasan/init.c                      |  8 +++++++-
> >>   mm/sparse-vmemmap.c                  |  5 +++++
> >>   8 files changed, 55 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/arch/loongarch/include/asm/pgalloc.h b/arch/loongarch/include/asm/pgalloc.h
> >> index 4e2d6b7ca2ee..b2698c03dc2c 100644
> >> --- a/arch/loongarch/include/asm/pgalloc.h
> >> +++ b/arch/loongarch/include/asm/pgalloc.h
> >> @@ -10,8 +10,21 @@
> >>
> >>   #define __HAVE_ARCH_PMD_ALLOC_ONE
> >>   #define __HAVE_ARCH_PUD_ALLOC_ONE
> >> +#define __HAVE_ARCH_PTE_ALLOC_ONE_KERNEL
> >>   #include <asm-generic/pgalloc.h>
> >>
> >> +static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
> >> +{
> >> +       pte_t *pte;
> >> +
> >> +       pte = (pte_t *) __get_free_page(GFP_KERNEL);
> >> +       if (!pte)
> >> +               return NULL;
> >> +
> >> +       kernel_pte_init(pte);
> >> +       return pte;
> >> +}
> >> +
> >>   static inline void pmd_populate_kernel(struct mm_struct *mm,
> >>                                         pmd_t *pmd, pte_t *pte)
> >>   {
> >> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> >> index 9965f52ef65b..22e3a8f96213 100644
> >> --- a/arch/loongarch/include/asm/pgtable.h
> >> +++ b/arch/loongarch/include/asm/pgtable.h
> >> @@ -269,6 +269,7 @@ extern void set_pmd_at(struct mm_struct *mm, unsigned long addr, pmd_t *pmdp, pm
> >>   extern void pgd_init(void *addr);
> >>   extern void pud_init(void *addr);
> >>   extern void pmd_init(void *addr);
> >> +extern void kernel_pte_init(void *addr);
> >>
> >>   /*
> >>    * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
> >> diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> >> index 8a87a482c8f4..9f26e933a8a3 100644
> >> --- a/arch/loongarch/mm/init.c
> >> +++ b/arch/loongarch/mm/init.c
> >> @@ -198,9 +198,11 @@ pte_t * __init populate_kernel_pte(unsigned long addr)
> >>          if (!pmd_present(pmdp_get(pmd))) {
> >>                  pte_t *pte;
> >>
> >> -               pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> >> +               pte = memblock_alloc_raw(PAGE_SIZE, PAGE_SIZE);
> >>                  if (!pte)
> >>                          panic("%s: Failed to allocate memory\n", __func__);
> >> +
> >> +               kernel_pte_init(pte);
> >>                  pmd_populate_kernel(&init_mm, pmd, pte);
> >>          }
> >>
> >> diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
> >> index 427d6b1aec09..34988573b0d5 100644
> >> --- a/arch/loongarch/mm/kasan_init.c
> >> +++ b/arch/loongarch/mm/kasan_init.c
> >> @@ -152,6 +152,8 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
> >>                  phys_addr_t page_phys = early ?
> >>                                          __pa_symbol(kasan_early_shadow_page)
> >>                                                : kasan_alloc_zeroed_page(node);
> >> +               if (!early)
> >> +                       kernel_pte_init(__va(page_phys));
> >>                  next = addr + PAGE_SIZE;
> >>                  set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
> >>          } while (ptep++, addr = next, addr != end && __pte_none(early, ptep_get(ptep)));
> >> @@ -287,7 +289,7 @@ void __init kasan_init(void)
> >>                  set_pte(&kasan_early_shadow_pte[i],
> >>                          pfn_pte(__phys_to_pfn(__pa_symbol(kasan_early_shadow_page)), PAGE_KERNEL_RO));
> >>
> >> -       memset(kasan_early_shadow_page, 0, PAGE_SIZE);
> >> +       kernel_pte_init(kasan_early_shadow_page);
> >>          csr_write64(__pa_symbol(swapper_pg_dir), LOONGARCH_CSR_PGDH);
> >>          local_flush_tlb_all();
> >>
> >> diff --git a/arch/loongarch/mm/pgtable.c b/arch/loongarch/mm/pgtable.c
> >> index eb6a29b491a7..228ffc1db0a3 100644
> >> --- a/arch/loongarch/mm/pgtable.c
> >> +++ b/arch/loongarch/mm/pgtable.c
> >> @@ -38,6 +38,28 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
> >>   }
> >>   EXPORT_SYMBOL_GPL(pgd_alloc);
> >>
> >> +void kernel_pte_init(void *addr)
> >> +{
> >> +       unsigned long *p, *end;
> >> +       unsigned long entry;
> >> +
> >> +       entry = (unsigned long)_PAGE_GLOBAL;
> >> +       p = (unsigned long *)addr;
> >> +       end = p + PTRS_PER_PTE;
> >> +
> >> +       do {
> >> +               p[0] = entry;
> >> +               p[1] = entry;
> >> +               p[2] = entry;
> >> +               p[3] = entry;
> >> +               p[4] = entry;
> >> +               p += 8;
> >> +               p[-3] = entry;
> >> +               p[-2] = entry;
> >> +               p[-1] = entry;
> >> +       } while (p != end);
> >> +}
> >> +
> >>   void pgd_init(void *addr)
> >>   {
> >>          unsigned long *p, *end;
> >> diff --git a/include/linux/mm.h b/include/linux/mm.h
> >> index ecf63d2b0582..6909fe059a2c 100644
> >> --- a/include/linux/mm.h
> >> +++ b/include/linux/mm.h
> >> @@ -3818,6 +3818,7 @@ void *sparse_buffer_alloc(unsigned long size);
> >>   struct page * __populate_section_memmap(unsigned long pfn,
> >>                  unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
> >>                  struct dev_pagemap *pgmap);
> >> +void kernel_pte_init(void *addr);
> >>   void pmd_init(void *addr);
> >>   void pud_init(void *addr);
> >>   pgd_t *vmemmap_pgd_populate(unsigned long addr, int node);
> >> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> >> index 89895f38f722..ac607c306292 100644
> >> --- a/mm/kasan/init.c
> >> +++ b/mm/kasan/init.c
> >> @@ -106,6 +106,10 @@ static void __ref zero_pte_populate(pmd_t *pmd, unsigned long addr,
> >>          }
> >>   }
> >>
> >> +void __weak __meminit kernel_pte_init(void *addr)
> >> +{
> >> +}
> >> +
> >>   static int __ref zero_pmd_populate(pud_t *pud, unsigned long addr,
> >>                                  unsigned long end)
> >>   {
> >> @@ -126,8 +130,10 @@ static int __ref zero_pmd_populate(pud_t *pud, unsigned long addr,
> >>
> >>                          if (slab_is_available())
> >>                                  p = pte_alloc_one_kernel(&init_mm);
> >> -                       else
> >> +                       else {
> >>                                  p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
> >> +                               kernel_pte_init(p);
> >> +                       }
> >>                          if (!p)
> >>                                  return -ENOMEM;
> >>
> >> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> >> index edcc7a6b0f6f..c0388b2e959d 100644
> >> --- a/mm/sparse-vmemmap.c
> >> +++ b/mm/sparse-vmemmap.c
> >> @@ -184,6 +184,10 @@ static void * __meminit vmemmap_alloc_block_zero(unsigned long size, int node)
> >>          return p;
> >>   }
> >>
> >> +void __weak __meminit kernel_pte_init(void *addr)
> >> +{
> >> +}
> >> +
> >>   pmd_t * __meminit vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node)
> >>   {
> >>          pmd_t *pmd = pmd_offset(pud, addr);
> >> @@ -191,6 +195,7 @@ pmd_t * __meminit vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node)
> >>                  void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
> >>                  if (!p)
> >>                          return NULL;
> >> +               kernel_pte_init(p);
> >>                  pmd_populate_kernel(&init_mm, pmd, p);
> >>          }
> >>          return pmd;
> >> --
> >> 2.39.3
> >>
>
>