[tip:x86/irq] x86/irq/64: Remove a hardcoded irq_stack_union access

[tip-bot for Andy Lutomirski]

Commit-ID:  4f44b8f0b33b7111216f0fad353315f796b81617
Gitweb:     https://git.kernel.org/tip/4f44b8f0b33b7111216f0fad353315f796b81617
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Sun, 14 Apr 2019 17:59:40 +0200
Committer:  Borislav Petkov <bp@xxxxxxx>
CommitDate: Wed, 17 Apr 2019 12:31:38 +0200

x86/irq/64: Remove a hardcoded irq_stack_union access

stack_overflow_check() is using both irq_stack_ptr and irq_stack_union
to find the IRQ stack. That's going to break when vmapped irq stacks are
introduced.

Change it to just use irq_stack_ptr.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Nicolai Stange <nstange@xxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190414160143.872549191@xxxxxxxxxxxxx
---
 arch/x86/kernel/irq_64.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index b50ac9c7397b..f6dcc8fea5c0 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -55,9 +55,8 @@ static inline void stack_overflow_check(struct pt_regs *regs)
 	    regs->sp <= curbase + THREAD_SIZE)
 		return;
 
-	irq_stack_top = (u64)this_cpu_ptr(irq_stack_union.irq_stack) +
-			STACK_TOP_MARGIN;
 	irq_stack_bottom = (u64)__this_cpu_read(irq_stack_ptr);
+	irq_stack_top = irq_stack_bottom - IRQ_STACK_SIZE + STACK_TOP_MARGIN;
 	if (regs->sp >= irq_stack_top && regs->sp <= irq_stack_bottom)
 		return;