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

maobibo <maobibo@xxxxxxxxxxx> · Fri, 18 Oct 2024 11:44:20 +0800

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()?

Regards
Bibo Mao
Huacai

On Mon, Oct 14, 2024 at 11:59 AM Bibo Mao <maobibo@xxxxxxxxxxx> 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@xxxxxxxxxxx>
---
  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









