Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table entry aware

[Christophe Leroy]

Le 08/09/2020 à 09:46, Alexander Gordeev a écrit :
On Tue, Sep 08, 2020 at 07:14:38AM +0200, Christophe Leroy wrote:
You forgot arch/powerpc/mm/book3s64/subpage_prot.c it seems.

Yes, and also two more sources :/
        arch/powerpc/mm/kasan/8xx.c
        arch/powerpc/mm/kasan/kasan_init_32.c

But these two are not quite obvious wrt pgd_addr_end() used
while traversing pmds. Could you please clarify a bit?


diff --git a/arch/powerpc/mm/kasan/8xx.c b/arch/powerpc/mm/kasan/8xx.c
index 2784224..89c5053 100644
--- a/arch/powerpc/mm/kasan/8xx.c
+++ b/arch/powerpc/mm/kasan/8xx.c
@@ -15,8 +15,8 @@
        for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd += 2, block 
+= SZ_8M) {
                pte_basic_t *new;
  
-		k_next = pgd_addr_end(k_cur, k_end);
-               k_next = pgd_addr_end(k_next, k_end);
+               k_next = pmd_addr_end(k_cur, k_end);
+               k_next = pmd_addr_end(k_next, k_end);

No, I don't think so.
On powerpc32 we have only two levels, so pgd and pmd are more or less 
the same.
But pmd_addr_end() as defined in include/asm-generic/pgtable-nopmd.h is 
a no-op, so I don't think it will work.

It is likely that this function should iterate on pgd, then you get pmd 
= pmd_offset(pud_offset(p4d_offset(pgd)));

                if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
                        continue;
  
diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
index fb29404..3f7d6dc6 100644
--- a/arch/powerpc/mm/kasan/kasan_init_32.c
+++ b/arch/powerpc/mm/kasan/kasan_init_32.c
@@ -38,7 +38,7 @@ int __init kasan_init_shadow_page_tables(unsigned long 
k_start, unsigned long k_
        for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd++) {
                pte_t *new;
  
-		k_next = pgd_addr_end(k_cur, k_end);
+               k_next = pmd_addr_end(k_cur, k_end);

Same here I get, iterate on pgd then get pmd = 
pmd_offset(pud_offset(p4d_offset(pgd)));

                if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
                        continue;
  
@@ -196,7 +196,7 @@ void __init kasan_early_init(void)
        kasan_populate_pte(kasan_early_shadow_pte, PAGE_KERNEL);
  
  	do {
-               next = pgd_addr_end(addr, end);
+               next = pmd_addr_end(addr, end);
                pmd_populate_kernel(&init_mm, pmd, kasan_early_shadow_pte);
        } while (pmd++, addr = next, addr != end);
  


Christophe