From 7f3ee97fda684c00c6c1a93437c901519af538da Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Fri, 3 Dec 2021 19:07:10 +0000
Subject: [PATCH] amd64: Set %fs selector more nonzeroly.

---
 sys/arch/amd64/acpi/acpi_wakeup_low.S | 1 +
 sys/arch/amd64/amd64/locore.S         | 4 ++--
 sys/arch/amd64/amd64/machdep.c        | 6 +++---
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/sys/arch/amd64/acpi/acpi_wakeup_low.S b/sys/arch/amd64/acpi/acpi_wakeup_low.S
index d1fd735c7647..f78fa70ffcb1 100644
--- a/sys/arch/amd64/acpi/acpi_wakeup_low.S
+++ b/sys/arch/amd64/acpi/acpi_wakeup_low.S
@@ -43,6 +43,7 @@ ENTRY(acpi_md_sleep_exit)
 	movw	$GSEL(GUDATA_SEL, SEL_UPL),%ax
 	movw	%ax,%ds
 	movw	%ax,%es
+	movw	%ax,%fs		/* AMD bug */
 	movw	$GSEL(GDATA_SEL, SEL_KPL),%ax
 	movw	%ax,%ss
 
diff --git a/sys/arch/amd64/amd64/locore.S b/sys/arch/amd64/amd64/locore.S
index ce4b281e30b3..014a5734630d 100644
--- a/sys/arch/amd64/amd64/locore.S
+++ b/sys/arch/amd64/amd64/locore.S
@@ -898,7 +898,7 @@ longmode_hi:
 
 	xorw	%ax,%ax
 	movw	%ax,%gs
-	movw	%ax,%fs
+	movw    %ax,%fs
 
 	/* The first physical page available. */
 	leaq	(TABLESIZE)(%rsi),%rdi
@@ -1267,8 +1267,8 @@ ENTRY(cpu_switchto)
 	movq	$GSEL(GUDATA_SEL, SEL_UPL),%rax
 	movw	%ax,%ds
 	movw	%ax,%es
+	movw	%ax,%fs		/* AMD bug */
 	xorq	%rax,%rax
-	movw	%ax,%fs
 	CLI(cx)
 	SWAPGS
 	movw	%ax,%gs
diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index fd84be2bf207..72cee7beeba5 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -454,7 +454,7 @@ x86_64_tls_switch(struct lwp *l)
 		update_descriptor(&ci->ci_gdt[GUGS_SEL], &zero);
 		setds(GSEL(GUDATA_SEL, SEL_UPL));
 		setes(GSEL(GUDATA_SEL, SEL_UPL));
-		setfs(0);
+		setfs(GSEL(GUDATA_SEL, SEL_UPL));
 		HYPERVISOR_set_segment_base(SEGBASE_GS_USER_SEL, 0);
 		HYPERVISOR_set_segment_base(SEGBASE_FS, pcb->pcb_fs);
 		HYPERVISOR_set_segment_base(SEGBASE_GS_USER, pcb->pcb_gs);
@@ -2256,7 +2256,7 @@ cpu_segregs64_zero(struct lwp *l)
 	tf->tf_gs = 0;
 	setds(GSEL(GUDATA_SEL, SEL_UPL));
 	setes(GSEL(GUDATA_SEL, SEL_UPL));
-	setfs(0);
+	setfs(GSEL(GUDATA_SEL, SEL_UPL));
 	setusergs(0);
 
 #ifndef XENPV
@@ -2294,7 +2294,7 @@ cpu_segregs32_zero(struct lwp *l)
 	tf->tf_gs = 0;
 	setds(GSEL(GUDATA32_SEL, SEL_UPL));
 	setes(GSEL(GUDATA32_SEL, SEL_UPL));
-	setfs(0);
+	setfs(GSEL(GUDATA32_SEL, SEL_UPL));
 	setusergs(0);
 	pcb->pcb_fs = 0;
 	pcb->pcb_gs = 0;