[PATCH] arm64: pgtable: make __pte_to_phys/__phys_to_pte_val inline functions

[PATCH] arm64: pgtable: make __pte_to_phys/__phys_to_pte_val inline functions

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

gcc warns about undefined behavior the vmalloc code when building
with CONFIG_ARM64_PA_BITS_52, when the 'idx++' in the argument to
__phys_to_pte_val() is evaluated twice:

mm/vmalloc.c: In function 'vmap_pfn_apply':
mm/vmalloc.c:2800:58: error: operation on 'data->idx' may be undefined [-Werror=sequence-point]
 2800 |         *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot));
      |                                                 ~~~~~~~~~^~
arch/arm64/include/asm/pgtable-types.h:25:37: note: in definition of macro '__pte'
   25 | #define __pte(x)        ((pte_t) { (x) } )
      |                                     ^
arch/arm64/include/asm/pgtable.h:80:15: note: in expansion of macro '__phys_to_pte_val'
   80 |         __pte(__phys_to_pte_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot))
      |               ^~~~~~~~~~~~~~~~~
mm/vmalloc.c:2800:30: note: in expansion of macro 'pfn_pte'
 2800 |         *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot));
      |                              ^~~~~~~

I have no idea why this never showed up earlier, but the safest
workaround appears to be changing those macros into inline functions
so the arguments get evaluated only once.

Cc: Matthew Wilcox <willy@infradead.org>
Fixes: 75387b92635e ("arm64: handle 52-bit physical addresses in page table entries")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/arm64/include/asm/pgtable.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 84fbb52b4224..c4ba047a82d2 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -67,9 +67,15 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
  * page table entry, taking care of 52-bit addresses.
  */
 #ifdef CONFIG_ARM64_PA_BITS_52
-#define __pte_to_phys(pte)	\
-	((pte_val(pte) & PTE_ADDR_LOW) | ((pte_val(pte) & PTE_ADDR_HIGH) << 36))
-#define __phys_to_pte_val(phys)	(((phys) | ((phys) >> 36)) & PTE_ADDR_MASK)
+static inline phys_addr_t __pte_to_phys(pte_t pte)
+{
+	return (pte_val(pte) & PTE_ADDR_LOW) |
+		((pte_val(pte) & PTE_ADDR_HIGH) << 36);
+}
+static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
+{
+	return (phys | (phys >> 36)) & PTE_ADDR_MASK;
+}
 #else
 #define __pte_to_phys(pte)	(pte_val(pte) & PTE_ADDR_MASK)
 #define __phys_to_pte_val(phys)	(phys)
-- 
2.29.2

Re: [PATCH] arm64: pgtable: make __pte_to_phys/__phys_to_pte_val inline functions

[Will Deacon]

On Fri, 5 Nov 2021 08:54:03 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> gcc warns about undefined behavior the vmalloc code when building
> with CONFIG_ARM64_PA_BITS_52, when the 'idx++' in the argument to
> __phys_to_pte_val() is evaluated twice:
> 
> mm/vmalloc.c: In function 'vmap_pfn_apply':
> mm/vmalloc.c:2800:58: error: operation on 'data->idx' may be undefined [-Werror=sequence-point]
>  2800 |         *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot));
>       |                                                 ~~~~~~~~~^~
> arch/arm64/include/asm/pgtable-types.h:25:37: note: in definition of macro '__pte'
>    25 | #define __pte(x)        ((pte_t) { (x) } )
>       |                                     ^
> arch/arm64/include/asm/pgtable.h:80:15: note: in expansion of macro '__phys_to_pte_val'
>    80 |         __pte(__phys_to_pte_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot))
>       |               ^~~~~~~~~~~~~~~~~
> mm/vmalloc.c:2800:30: note: in expansion of macro 'pfn_pte'
>  2800 |         *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot));
>       |                              ^~~~~~~
> 
> [...]

Applied to arm64 (for-next/core), thanks!

[1/1] arm64: pgtable: make __pte_to_phys/__phys_to_pte_val inline functions
      https://git.kernel.org/arm64/c/c7c386fbc202

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev