linux-kernel - [PATCH v5 1/7] x86,mm: Ensure correct alignment of the fixmap

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Date:	Mon,  5 May 2014 12:19:31 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...capital.net>
Subject: [PATCH v5 1/7] x86,mm: Ensure correct alignment of the fixmap

The early_ioremap code requires that its buffers not span a PMD
boundary.  The logic for ensuring that only works if the fixmap is
aligned, so assert that it's aligned correctly.

To make this work reliably, reserve_top_address needs to be
adjusted.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
 arch/x86/mm/ioremap.c | 6 ++++++
 arch/x86/mm/pgtable.c | 6 +++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 597ac15..6ef98c5 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -355,6 +355,12 @@ void __init early_ioremap_init(void)
 {
 	pmd_t *pmd;
 
+#ifdef CONFIG_X86_64
+	BUILD_BUG_ON((fix_to_virt(0) + PAGE_SIZE) & ((1 << PMD_SHIFT) - 1));
+#else
+	WARN_ON((fix_to_virt(0) + PAGE_SIZE) & ((1 << PMD_SHIFT) - 1));
+#endif
+
 	early_ioremap_setup();
 
 	pmd = early_ioremap_pmd(fix_to_virt(FIX_BTMAP_BEGIN));
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index c96314a..5f8bdda 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -449,9 +449,9 @@ void __init reserve_top_address(unsigned long reserve)
 {
 #ifdef CONFIG_X86_32
 	BUG_ON(fixmaps_set > 0);
-	printk(KERN_INFO "Reserving virtual address space above 0x%08x\n",
-	       (int)-reserve);
-	__FIXADDR_TOP = -reserve - PAGE_SIZE;
+	__FIXADDR_TOP = round_down(-reserve, 1 << PMD_SHIFT) - PAGE_SIZE;
+	printk(KERN_INFO "Reserving virtual address space above 0x%08lx (rounded to 0x%08lx)\n",
+	       -reserve, __FIXADDR_TOP + PAGE_SIZE);
 #endif
 }
 
-- 
1.9.0

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