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Date:   Wed, 15 Sep 2021 17:19:17 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     =?utf-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
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Subject: [PATCH] x86: Increase exception stack sizes
Message-ID: <YUIO9Ye98S5Eb68w@hirez.programming.kicks-ass.net>
References: <d16e7188-1afa-7513-990c-804811747bcb@linux.alibaba.com>
 <d85f9710-67c9-2573-07c4-05d9c677d615@intel.com>
 <d8853e49-8b34-4632-3e29-012eb605bea9@linux.alibaba.com>
 <09777a57-a771-5e17-7e17-afc03ea9b83b@linux.alibaba.com>
 <4f63c8bc-1d09-1717-cf81-f9091a9f9fb0@linux.alibaba.com>
 <18252e42-9c30-73d4-e3bb-0e705a78af41@intel.com>
 <4cba7088-f7c8-edcf-02cd-396eb2a56b46@linux.alibaba.com>
 <bbe09ffb-08b7-824c-943f-dffef51e98c2@intel.com>
 <ac31b8c7-122e-3467-566b-54f053ca0ae2@linux.alibaba.com>
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On Wed, Sep 15, 2021 at 03:34:20PM +0800, 王贇 wrote:
> Hi, Dave, Peter
> 
> What if we just increase the stack size when ftrace enabled?

I think we can do an unconditional increase. But please first test that
guard page patch :-)

---
Subject: x86: Increase exception stack sizes
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Sep 15 16:19:46 CEST 2021

It turns out that a single page of stack is trivial to overflow with
all the tracing gunk enabled. Raise the exception stacks to 2 pages,
which is still half the interrupt stacks, which are at 4 pages.

Reported-by: Michael Wang <yun.wang@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/page_64_types.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -15,7 +15,7 @@
 #define THREAD_SIZE_ORDER	(2 + KASAN_STACK_ORDER)
 #define THREAD_SIZE  (PAGE_SIZE << THREAD_SIZE_ORDER)
 
-#define EXCEPTION_STACK_ORDER (0 + KASAN_STACK_ORDER)
+#define EXCEPTION_STACK_ORDER (1 + KASAN_STACK_ORDER)
 #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
 
 #define IRQ_STACK_ORDER (2 + KASAN_STACK_ORDER)