* Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> Separating out the assembler-compatible defines from the types
> headers appears to be a bigger patch, since it's all mixed in with C
> syntax:
>
> <=-----------------------------------===============================
> typedef struct { pud_t pud; } pmd_t;
>
> #define PMD_SHIFT PUD_SHIFT
> #define PTRS_PER_PMD 1
> #define PMD_SIZE (1UL << PMD_SHIFT)
> #define PMD_MASK (~(PMD_SIZE-1))
>
> /*
> * The "pud_xxx()" functions here are trivial for a folded two-level
> * setup: the pmd is never bad, and a pmd always exists (as it's folded
> * into the pud entry)
> */
> static inline int pud_none(pud_t pud) { return 0; }
> static inline int pud_bad(pud_t pud) { return 0; }
> static inline int pud_present(pud_t pud) { return 1; }
> ================================================================>
>
> In any case I've removed the commit for the time being until this all
> is cleared up.
So there's a simple solution: define it on i386 too, via the patch
below. It appears the double-definition doesn't create any warnings, on
GCC at least.
But if it's an issue, we could do something like this in
<asm-generic/pgtable-nopmd.h>:
#if defined(PTRS_PER_PMD) && (PTRS_PER_PMD != 1)
# error "mm: Wait a minute, that's a super confusing pagetable setup ..."
#endif
?
Thanks,
Ingo
=========================>
From: Ingo Molnar <mingo@xxxxxxxxxx>
Date: Thu, 6 Mar 2025 22:53:49 +0100
Subject: [PATCH] x86/mm: Define PTRS_PER_PMD for assembly code too
Andy reported the following build warning from head_32.S:
In file included from arch/x86/kernel/head_32.S:29:
arch/x86/include/asm/pgtable_32.h:59:5: error: "PTRS_PER_PMD" is not defined, evaluates to 0 [-Werror=undef]
59 | #if PTRS_PER_PMD > 1
The reason is that on 2-level i386 paging the folded in PMD's
PTRS_PER_PMD constant is not defined in assembly headers,
only in generic MM C headers.
Instead of trying to fish out the definition from the generic
headers, just define it - it even has a comment for it already...
Reported-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/pgtable-2level_types.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/pgtable-2level_types.h b/arch/x86/include/asm/pgtable-2level_types.h
index 7f6ccff0ba72..4a12c276b181 100644
--- a/arch/x86/include/asm/pgtable-2level_types.h
+++ b/arch/x86/include/asm/pgtable-2level_types.h
@@ -23,17 +23,17 @@ typedef union {
#define ARCH_PAGE_TABLE_SYNC_MASK PGTBL_PMD_MODIFIED
/*
- * traditional i386 two-level paging structure:
+ * Traditional i386 two-level paging structure:
*/
#define PGDIR_SHIFT 22
#define PTRS_PER_PGD 1024
-
/*
- * the i386 is two-level, so we don't really have any
- * PMD directory physically.
+ * The i386 is two-level, so we don't really have any
+ * PMD directory physically:
*/
+#define PTRS_PER_PMD 1
#define PTRS_PER_PTE 1024
|