[RFC PATCH 23/32] x86/fred: update MSR_IA32_FRED_RSP0 during task switch

[Xin Li <xin3.li@intel.com>]

From: "H. Peter Anvin (Intel)" <hpa@zytor.com>

MSR_IA32_FRED_RSP0 is used during ring 3 event delivery, and needs to
be updated to point to the top of next task stack during task switch.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
 arch/x86/include/asm/switch_to.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index c08eb0fdd11f..c28170d4fbba 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -71,9 +71,13 @@ static inline void update_task_stack(struct task_struct *task)
 	else
 		this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
 #else
-	/* Xen PV enters the kernel on the thread stack. */
-	if (static_cpu_has(X86_FEATURE_XENPV))
+	if (cpu_feature_enabled(X86_FEATURE_FRED)) {
+		wrmsrl(MSR_IA32_FRED_RSP0,
+		       task_top_of_stack(task) + TOP_OF_KERNEL_STACK_PADDING);
+	} else if (static_cpu_has(X86_FEATURE_XENPV)) {
+		/* Xen PV enters the kernel on the thread stack. */
 		load_sp0(task_top_of_stack(task));
+	}
 #endif
 }
 
-- 
2.34.1