[PATCH] x86/head64: use pointer type in sizeof

[PATCH] x86/head64: use pointer type in sizeof

[Alexander Kuleshov]

We changed loops with memset in the 5e9ebbd87a99 commit (x86/boot:
Micro-optimize reset_early_page_tables()). The base for size of
memset was size of pud_p/pmd_p, but the they are actually
represented as pointers, although they have the same sizes.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
---
based on x86/tip/boot

 arch/x86/kernel/head64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 35843ca..7793a17 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -75,7 +75,7 @@ again:
 		}
 
 		pud_p = (pudval_t *)early_dynamic_pgts[next_early_pgt++];
-		memset(pud_p, 0, sizeof(pud_p) * PTRS_PER_PUD);
+		memset(pud_p, 0, sizeof(*pud_p) * PTRS_PER_PUD);
 		*pgd_p = (pgdval_t)pud_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
 	}
 	pud_p += pud_index(address);
@@ -90,7 +90,7 @@ again:
 		}
 
 		pmd_p = (pmdval_t *)early_dynamic_pgts[next_early_pgt++];
-		memset(pmd_p, 0, sizeof(pmd_p) * PTRS_PER_PMD);
+		memset(pmd_p, 0, sizeof(*pmd_p) * PTRS_PER_PMD);
 		*pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
 	}
 	pmd = (physaddr & PMD_MASK) + early_pmd_flags;
-- 
2.7.0.25.gfc10eb5

Re: [PATCH] x86/head64: use pointer type in sizeof

[Ingo Molnar]

* Alexander Kuleshov <kuleshovmail@gmail.com> wrote:

> We changed loops with memset in the 5e9ebbd87a99 commit (x86/boot:
> Micro-optimize reset_early_page_tables()). The base for size of
> memset was size of pud_p/pmd_p, but the they are actually
> represented as pointers, although they have the same sizes.

That's rather confused. Also the title is confused:

  x86/head64: use pointer type in sizeof

what the fix does it to _not_ use a pointer type.

I fixed the title and the changelog, but you really need to be more careful...

Thanks,

	Ingo

[tip:x86/boot] x86/boot: Use proper array element type in memset( ) size calculation

[tip-bot for Alexander Kuleshov]

Commit-ID:  a91bbe017552b80e12d712c85549b933a62c6ed4
Gitweb:     http://git.kernel.org/tip/a91bbe017552b80e12d712c85549b933a62c6ed4
Author:     Alexander Kuleshov <kuleshovmail@gmail.com>
AuthorDate: Tue, 9 Feb 2016 19:44:54 +0600
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 9 Feb 2016 14:55:48 +0100

x86/boot: Use proper array element type in memset() size calculation

I changed open coded zeroing loops to explicit memset()s in the
following commit:

  5e9ebbd87a99 ("x86/boot: Micro-optimize reset_early_page_tables()")

The base for the size argument of memset was sizeof(pud_p/pmd_p), which
are pointers - but the initialized array has pud_t/pmd_t elements.

Luckily the two types had the same size, so this did not result in any
runtime misbehavior.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: Alexander Popov <alpopov@ptsecurity.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1455025494-4063-1-git-send-email-kuleshovmail@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/head64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 35843ca..7793a17 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -75,7 +75,7 @@ again:
 		}
 
 		pud_p = (pudval_t *)early_dynamic_pgts[next_early_pgt++];
-		memset(pud_p, 0, sizeof(pud_p) * PTRS_PER_PUD);
+		memset(pud_p, 0, sizeof(*pud_p) * PTRS_PER_PUD);
 		*pgd_p = (pgdval_t)pud_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
 	}
 	pud_p += pud_index(address);
@@ -90,7 +90,7 @@ again:
 		}
 
 		pmd_p = (pmdval_t *)early_dynamic_pgts[next_early_pgt++];
-		memset(pmd_p, 0, sizeof(pmd_p) * PTRS_PER_PMD);
+		memset(pmd_p, 0, sizeof(*pmd_p) * PTRS_PER_PMD);
 		*pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
 	}
 	pmd = (physaddr & PMD_MASK) + early_pmd_flags;