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

Commit-ID:     11cff44c45f797cb7e3f75bfb9610d6b2a89ad3a
Gitweb:        https://git.kernel.org/tip/11cff44c45f797cb7e3f75bfb9610d6b2a89ad3a
Author:        Juergen Gross <jgross@suse.com>
AuthorDate:    Mon, 19 Jan 2026 19:26:28 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Sat, 21 Mar 2026 12:36:41 +01:00

x86/paravirt: Replace io_delay() hook with a bool

The io_delay() paravirt hook is in no way performance critical and all users
setting it to a different function than native_io_delay() are using an empty
function as replacement.

Allow replacing the hook with a bool indicating whether native_io_delay()
should be called.

  [ bp: Massage commit message. ]

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20260119182632.596369-3-jgross@suse.com
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/include/asm/io.h             |  9 ++++++---
 arch/x86/include/asm/paravirt-base.h  |  6 ++++++
 arch/x86/include/asm/paravirt.h       | 11 -----------
 arch/x86/include/asm/paravirt_types.h |  2 --
 arch/x86/kernel/cpu/vmware.c          |  2 +-
 arch/x86/kernel/kvm.c                 |  8 +-------
 arch/x86/kernel/paravirt.c            |  3 +--
 arch/x86/xen/enlighten_pv.c           |  6 +-----
 8 files changed, 16 insertions(+), 31 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 2ea2574..4179a2e 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -242,11 +242,16 @@ extern int io_delay_type;
 extern void io_delay_init(void);
 
 #if defined(CONFIG_PARAVIRT)
-#include <asm/paravirt.h>
+#include <asm/paravirt-base.h>
 #else
+#define call_io_delay() true
+#endif
 
 static inline void slow_down_io(void)
 {
+	if (!call_io_delay())
+		return;
+
 	native_io_delay();
 #ifdef REALLY_SLOW_IO
 	native_io_delay();
@@ -255,8 +260,6 @@ static inline void slow_down_io(void)
 #endif
 }
 
-#endif
-
 #define BUILDIO(bwl, type)						\
 static inline void out##bwl##_p(type value, u16 port)			\
 {									\
diff --git a/arch/x86/include/asm/paravirt-base.h b/arch/x86/include/asm/paravirt-base.h
index 982a0b9..3b9e777 100644
--- a/arch/x86/include/asm/paravirt-base.h
+++ b/arch/x86/include/asm/paravirt-base.h
@@ -15,6 +15,8 @@ struct pv_info {
 #ifdef CONFIG_PARAVIRT_XXL
 	u16 extra_user_64bit_cs;  /* __USER_CS if none */
 #endif
+	bool io_delay;
+
 	const char *name;
 };
 
@@ -26,6 +28,10 @@ u64 _paravirt_ident_64(u64);
 #endif
 #define paravirt_nop	((void *)nop_func)
 
+#ifdef CONFIG_PARAVIRT
+#define call_io_delay() pv_info.io_delay
+#endif
+
 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 void paravirt_set_cap(void);
 #else
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index fcf8ab5..cdfe400 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -19,17 +19,6 @@
 #include <linux/cpumask.h>
 #include <asm/frame.h>
 
-/* The paravirtualized I/O functions */
-static inline void slow_down_io(void)
-{
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-#ifdef REALLY_SLOW_IO
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-#endif
-}
-
 void native_flush_tlb_local(void);
 void native_flush_tlb_global(void);
 void native_flush_tlb_one_user(unsigned long addr);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 9bcf6bc..4f5ae00 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -30,8 +30,6 @@ struct pv_lazy_ops {
 
 struct pv_cpu_ops {
 	/* hooks for various privileged instructions */
-	void (*io_delay)(void);
-
 #ifdef CONFIG_PARAVIRT_XXL
 	unsigned long (*get_debugreg)(int regno);
 	void (*set_debugreg)(int regno, unsigned long value);
diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index a3e6936..eee0d1a 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -339,7 +339,7 @@ arch_initcall(activate_jump_labels);
 static void __init vmware_paravirt_ops_setup(void)
 {
 	pv_info.name = "VMware hypervisor";
-	pv_ops.cpu.io_delay = paravirt_nop;
+	pv_info.io_delay = false;
 
 	if (vmware_tsc_khz == 0)
 		return;
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 3bc0623..29226d1 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -75,12 +75,6 @@ DEFINE_PER_CPU_DECRYPTED(struct kvm_steal_time, steal_time) __aligned(64) __visi
 static int has_steal_clock = 0;
 
 static int has_guest_poll = 0;
-/*
- * No need for any "IO delay" on KVM
- */
-static void kvm_io_delay(void)
-{
-}
 
 #define KVM_TASK_SLEEP_HASHBITS 8
 #define KVM_TASK_SLEEP_HASHSIZE (1<<KVM_TASK_SLEEP_HASHBITS)
@@ -327,7 +321,7 @@ static void __init paravirt_ops_setup(void)
 	pv_info.name = "KVM";
 
 	if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
-		pv_ops.cpu.io_delay = kvm_io_delay;
+		pv_info.io_delay = false;
 
 #ifdef CONFIG_X86_IO_APIC
 	no_timer_check = 1;
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index a6ed52c..792fa96 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -94,6 +94,7 @@ struct pv_info pv_info = {
 #ifdef CONFIG_PARAVIRT_XXL
 	.extra_user_64bit_cs = __USER_CS,
 #endif
+	.io_delay = true,
 };
 
 /* 64-bit pagetable entries */
@@ -101,8 +102,6 @@ struct pv_info pv_info = {
 
 struct paravirt_patch_template pv_ops = {
 	/* Cpu ops. */
-	.cpu.io_delay		= native_io_delay,
-
 #ifdef CONFIG_PARAVIRT_XXL
 	.cpu.cpuid		= native_cpuid,
 	.cpu.get_debugreg	= pv_native_get_debugreg,
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 6e459e4..0a6a50f 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1045,10 +1045,6 @@ static void xen_update_io_bitmap(void)
 }
 #endif
 
-static void xen_io_delay(void)
-{
-}
-
 static DEFINE_PER_CPU(unsigned long, xen_cr0_value);
 
 static unsigned long xen_read_cr0(void)
@@ -1208,6 +1204,7 @@ void __init xen_setup_vcpu_info_placement(void)
 
 static const struct pv_info xen_info __initconst = {
 	.extra_user_64bit_cs = FLAT_USER_CS64,
+	.io_delay = false,
 	.name = "Xen",
 };
 
@@ -1391,7 +1388,6 @@ asmlinkage __visible void __init xen_start_kernel(struct start_info *si)
 	pv_ops.cpu.invalidate_io_bitmap = xen_invalidate_io_bitmap;
 	pv_ops.cpu.update_io_bitmap = xen_update_io_bitmap;
 #endif
-	pv_ops.cpu.io_delay = xen_io_delay;
 	pv_ops.cpu.start_context_switch = xen_start_context_switch;
 	pv_ops.cpu.end_context_switch = xen_end_context_switch;