1). It can ensure the upper PAGE_SHIFT'ed bits of PHYS_PFN(..) are clear
by the C11 standard:
6.5.7 Bitwise shift operator
...
The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has
an unsigned type or if E1 has a signed type and a nonnegative value,
the value of the result is the integral part of the quotient of E1 / 2^E2.
@pfn parameter of pfn_valid(..) is unsigned long and PHYS_PFN(..) makes
the upper bits clear(zero) always with it. Otherwise, the result of E1 / 2^E2
doesn't make sense in the document.
2). x86 instructions
The following x86 instructions are the part of the redundant exception handler:
...
movabs $0xfffffffffffff,%rax
and %rdi,%rax
cmp %rax,%rdi
je 22
xor %eax,%eax
jmp __x86_return_thunk
22: push %rbp
...
%rdi would be the @pfn parameter of pfn_valid(..) and -1 assigned to %rax.
'je' always takes place by %rdi AND and CMP ops with %rax.
Therefore, the exception handler is unnecessary.
Signed-off-by: Leesoo Ahn <lsahn@xxxxxxxxxx>
---
include/linux/mmzone.h | 9 ---------
1 file changed, 9 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 17506e4a2835..164ae80977d6 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -2028,15 +2028,6 @@ static inline int pfn_valid(unsigned long pfn)
struct mem_section *ms;
int ret;
- /*
- * Ensure the upper PAGE_SHIFT bits are clear in the
- * pfn. Else it might lead to false positives when
- * some of the upper bits are set, but the lower bits
- * match a valid pfn.
- */
- if (PHYS_PFN(PFN_PHYS(pfn)) != pfn)
- return 0;
-
if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
return 0;
ms = __pfn_to_section(pfn);
--
2.46.0
