Re: [tip:x86/irq] x86: Always use irq stacks

["Alexander van Heukelum" <heukelum@fastmail.fm>]

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On Fri, 03 Sep 2010 17:00 +0200, "Ingo Molnar" <mingo@elte.hu> wrote:
> 
> * tip-bot for Christoph Hellwig <hch@lst.de> wrote:
> 
> > Commit-ID:  7974891db234467eaf1fec613ec0129cb4ac2332
> > Gitweb:     http://git.kernel.org/tip/7974891db234467eaf1fec613ec0129cb4ac2332
> > Author:     Christoph Hellwig <hch@lst.de>
> > AuthorDate: Mon, 28 Jun 2010 14:15:54 +0200
> > Committer:  Thomas Gleixner <tglx@linutronix.de>
> > CommitDate: Tue, 29 Jun 2010 12:12:59 +0200
> > 
> > x86: Always use irq stacks
>
> [...]
> 
> Checking out 7974891db2 and building+booting a kernel with this config 
> causes shows the crash.
> 
> Checking out 7974891db2~1 and building+booting a kernel with this config 
> gives a working system.
> 
> Note that tip:x86/irq has these commits currently:
> 
>  1813a68: x86: Move alloc_desk_mask variables inside ifdef
>  2589737: x86-32: Align IRQ stacks properly
>  dcfa726: x86: Remove CONFIG_4KSTACKS
>  7974891: x86: Always use irq stacks

Hello Ingo, Christoph, ...

There is still a problem with the alignment of the irq stacks. Maybe it's only
theoretical, but I think the attached patch is necessary. (Attached because
I'm sending it via a web interface.)

Please test and apply :).

Greetings,
    Alexander

> Thanks,
> 
> 	Ingo
> 


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From 1031da48a89aa437199af581169c65268f9bdbaa Mon Sep 17 00:00:00 2001
From: Alexander van Heukelum <heukelum@fastmail.fm>
Date: Mon, 6 Sep 2010 20:15:05 +0200
Subject: [PATCH] i386: Align percpu area and irq stacks to THREAD_SIZE

The irq stacks, located in the percpu-area, need to be THREAD_SIZE aligned. Add
the infrastucture to align percpu variables to larger-than-pagesize amounts within
the percpu area, and use it to specify the alignment for the irq stacks. Also
align the percpu area itself to THREAD_SIZE.

This should make irq stacks work with 8K THREAD_SIZE.

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
---
 arch/x86/kernel/irq_32.c      |    6 ++++--
 arch/x86/kernel/vmlinux.lds.S |    2 +-
 include/linux/percpu-defs.h   |   12 ++++++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 3b5609f..db7ebe6 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -60,8 +60,10 @@ union irq_ctx {
 static DEFINE_PER_CPU(union irq_ctx *, hardirq_ctx);
 static DEFINE_PER_CPU(union irq_ctx *, softirq_ctx);
 
-static DEFINE_PER_CPU_PAGE_ALIGNED(union irq_ctx, hardirq_stack);
-static DEFINE_PER_CPU_PAGE_ALIGNED(union irq_ctx, softirq_stack);
+static DEFINE_PER_CPU_MULTIPAGE_ALIGNED(union irq_ctx,
+		 hardirq_stack, THREAD_SIZE);
+static DEFINE_PER_CPU_MULTIPAGE_ALIGNED(union irq_ctx,
+		softirq_stack, THREAD_SIZE);
 
 static void call_on_stack(void *func, void *stack)
 {
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index d0bb522..bb89947 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -273,7 +273,7 @@ SECTIONS
 	}
 
 #if !defined(CONFIG_X86_64) || !defined(CONFIG_SMP)
-	PERCPU(PAGE_SIZE)
+	PERCPU(THREAD_SIZE)
 #endif
 
 	. = ALIGN(PAGE_SIZE);
diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
index ce2dc65..ab20d11 100644
--- a/include/linux/percpu-defs.h
+++ b/include/linux/percpu-defs.h
@@ -139,6 +139,18 @@
 	__aligned(PAGE_SIZE)
 
 /*
+ * Declaration/definition used for large per-CPU variables that must be
+ * aligned to something larger than the pagesize.
+ */
+#define DECLARE_PER_CPU_MULTIPAGE_ALIGNED(type, name, size)		\
+	DECLARE_PER_CPU_SECTION(type, name, "..page_aligned")		\
+	__aligned(size)
+
+#define DEFINE_PER_CPU_MULTIPAGE_ALIGNED(type, name, size)		\
+	DEFINE_PER_CPU_SECTION(type, name, "..page_aligned")		\
+	__aligned(size)
+
+/*
  * Intermodule exports for per-CPU variables.  sparse forgets about
  * address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
  * noop if __CHECKER__.
-- 
1.7.1