linux-kernel - [PATCH 12/35] x86/32: Use tss.sp1 as cpu_current_top_of

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Date:   Mon, 16 Apr 2018 17:25:00 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>,
        jroedel@...e.de, joro@...tes.org
Subject: [PATCH 12/35] x86/32: Use tss.sp1 as cpu_current_top_of_stack

From: Joerg Roedel <jroedel@...e.de>

Now that we store the task-stack in tss.sp1 we can also use
it as cpu_current_top_of_stack. This unifies the handling
with x86-64.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/include/asm/processor.h   | 4 ----
 arch/x86/include/asm/thread_info.h | 2 --
 arch/x86/kernel/cpu/common.c       | 4 ----
 arch/x86/kernel/process_32.c       | 6 ------
 4 files changed, 16 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 4fa4206..3894f63 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -374,12 +374,8 @@ DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss_rw);
 #define __KERNEL_TSS_LIMIT	\
 	(IO_BITMAP_OFFSET + IO_BITMAP_BYTES + sizeof(unsigned long) - 1)
 
-#ifdef CONFIG_X86_32
-DECLARE_PER_CPU(unsigned long, cpu_current_top_of_stack);
-#else
 /* The RO copy can't be accessed with this_cpu_xyz(), so use the RW copy. */
 #define cpu_current_top_of_stack cpu_tss_rw.x86_tss.sp1
-#endif
 
 /*
  * Save the original ist values for checking stack pointers during debugging
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index a5d9521..943c673 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -205,9 +205,7 @@ static inline int arch_within_stack_frames(const void * const stack,
 
 #else /* !__ASSEMBLY__ */
 
-#ifdef CONFIG_X86_64
 # define cpu_current_top_of_stack (cpu_tss_rw + TSS_sp1)
-#endif
 
 #endif
 
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 311e988..2d67ad0 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1512,10 +1512,6 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count);
  * the top of the kernel stack.  Use an extra percpu variable to track the
  * top of the kernel stack directly.
  */
-DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) =
-	(unsigned long)&init_thread_union + THREAD_SIZE;
-EXPORT_PER_CPU_SYMBOL(cpu_current_top_of_stack);
-
 #ifdef CONFIG_CC_STACKPROTECTOR
 DEFINE_PER_CPU_ALIGNED(struct stack_canary, stack_canary);
 #endif
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 3f3a8c6..8c29fd5 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -290,12 +290,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	update_sp0(next_p);
 	refresh_sysenter_cs(next);
 	this_cpu_write(cpu_current_top_of_stack, task_top_of_stack(next_p));
-	/*
-	 * TODO: Find a way to let cpu_current_top_of_stack point to
-	 * cpu_tss_rw.x86_tss.sp1. Doing so now results in stack corruption with
-	 * iret exceptions.
-	 */
-	this_cpu_write(cpu_tss_rw.x86_tss.sp1, next_p->thread.sp0);
 
 	/*
 	 * Restore %gs if needed (which is common)
-- 
2.7.4