[PATCH v7 22/33] x86/fred: update MSR_IA32_FRED_RSP0 during task switch

Xin Li
2023-04-04T10:55:42Z

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.

Update MSR_IA32_FRED_RSP0 with WRMSR instruction for now, and will use
WRMSRNS/WRMSRLIST for performance once it gets upstreamed.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
arch/x86/include/asm/switch_to.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 5c91305d09d2..00fd85abc1d2 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -68,9 +68,16 @@ static inline void update_task_stack(struct task_struct *task)
#ifdef CONFIG_X86_32
this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0);
#else
- /* Xen PV enters the kernel on the thread stack. */
- if (cpu_feature_enabled(X86_FEATURE_XENPV))
+ if (cpu_feature_enabled(X86_FEATURE_FRED)) {
+ /*
+ * Will use WRMSRNS/WRMSRLIST for performance once it's upstreamed.
+ */
+ wrmsrl(MSR_IA32_FRED_RSP0,
+ task_top_of_stack(task) + TOP_OF_KERNEL_STACK_PADDING);
+ } else if (cpu_feature_enabled(X86_FEATURE_XENPV)) {
+ /* Xen PV enters the kernel on the thread stack. */
load_sp0(task_top_of_stack(task));
+ }
#endif
}

--
2.34.1