[RFC 09/10] x86: Enable reclaimable stacks

[David Stevens <stevensd@google.com>]

Implement top_of_blocked_task_stack() to get the stack pointer out of
a thread_struct and enable HAVE_ARCH_RECLAIMABLE_STACK.

Signed-off-by: David Stevens <stevensd@google.com>
---
 arch/x86/Kconfig                 | 1 +
 arch/x86/include/asm/processor.h | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bdad90f210e4..652d5a9c0830 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -211,6 +211,7 @@ config X86
 	select HAVE_ARCH_USERFAULTFD_WP         if X86_64 && USERFAULTFD
 	select HAVE_ARCH_USERFAULTFD_MINOR	if X86_64 && USERFAULTFD
 	select HAVE_ARCH_VMAP_STACK		if X86_64
+	select HAVE_ARCH_RECLAIMABLE_STACK	if X86_64
 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
 	select HAVE_ARCH_WITHIN_STACK_FRAMES
 	select HAVE_ASM_MODVERSIONS
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 87b1d4c0727e..207e7adced64 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -690,6 +690,11 @@ extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
 #define GET_TSC_CTL(adr)	get_tsc_mode((adr))
 #define SET_TSC_CTL(val)	set_tsc_mode((val))
 
+static inline unsigned long top_of_blocked_task_stack(struct thread_struct *thread)
+{
+	return thread->sp;
+}
+
 extern int get_tsc_mode(unsigned long adr);
 extern int set_tsc_mode(unsigned int val);
 
-- 
2.55.0.897.gb25b4bd76c-goog