[tip: x86/fred] x86/fred: Update MSR_IA32_FRED_RSP0 during task switch

[tip-bot2 for H. Peter Anvin (Intel)]

The following commit has been merged into the x86/fred branch of tip:

Commit-ID:     9356c4b8886c4f7d3436c3f7fe31715bdcf1c79e
Gitweb:        https://git.kernel.org/tip/9356c4b8886c4f7d3436c3f7fe31715bdcf1c79e
Author:        H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
AuthorDate:    Tue, 05 Dec 2023 02:50:06 -08:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Wed, 31 Jan 2024 22:01:36 +01:00

x86/fred: Update MSR_IA32_FRED_RSP0 during task switch

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@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Link: https://lore.kernel.org/r/20231205105030.8698-18-xin3.li@xxxxxxxxx
---
 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 f42dbf1..c3bd0c0 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -70,9 +70,13 @@ 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)) {
+		/* WRMSRNS is a baseline feature for FRED. */
+		wrmsrns(MSR_IA32_FRED_RSP0, (unsigned long)task_stack_page(task) + THREAD_SIZE);
+	} 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
 }