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Message-ID: <20251126162018.5676-2-jgross@suse.com>
Date: Wed, 26 Nov 2025 17:20:14 +0100
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org,
x86@...nel.org,
virtualization@...ts.linux.dev,
kvm@...r.kernel.org
Cc: Juergen Gross <jgross@...e.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Ajay Kaher <ajay.kaher@...adcom.com>,
Alexey Makhalov <alexey.makhalov@...adcom.com>,
Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
xen-devel@...ts.xenproject.org
Subject: [PATCH 1/5] 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.
This enables to replace the hook with a bool indicating whether
native_io_delay() should be called.
Signed-off-by: Juergen Gross <jgross@...e.com>
---
arch/x86/include/asm/io.h | 7 +++++--
arch/x86/include/asm/paravirt.h | 11 +----------
arch/x86/include/asm/paravirt_types.h | 3 +--
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 +-----
7 files changed, 11 insertions(+), 29 deletions(-)
diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index ca309a3227c7..0448575569b9 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -245,9 +245,14 @@ extern void io_delay_init(void);
#if defined(CONFIG_PARAVIRT)
#include <asm/paravirt.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();
@@ -256,8 +261,6 @@ 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.h b/arch/x86/include/asm/paravirt.h
index b5e59a7ba0d0..0ab798d234cc 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -53,16 +53,7 @@ static inline u64 paravirt_steal_clock(int cpu)
void __init paravirt_set_cap(void);
#endif
-/* The paravirtualized I/O functions */
-static inline void slow_down_io(void)
-{
- PVOP_VCALL0(cpu.io_delay);
-#ifdef REALLY_SLOW_IO
- PVOP_VCALL0(cpu.io_delay);
- PVOP_VCALL0(cpu.io_delay);
- PVOP_VCALL0(cpu.io_delay);
-#endif
-}
+#define call_io_delay() pv_info.io_delay
void native_flush_tlb_local(void);
void native_flush_tlb_global(void);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 37a8627d8277..ee399f467796 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -36,6 +36,7 @@ struct pv_info {
#ifdef CONFIG_PARAVIRT_XXL
u16 extra_user_64bit_cs; /* __USER_CS if none */
#endif
+ bool io_delay;
const char *name;
};
@@ -51,8 +52,6 @@ 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 cb3f900c46fc..47db25d63c8d 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -338,7 +338,7 @@ 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 b67d7c59dca0..b02d441efa3b 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -73,12 +73,6 @@ 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)
@@ -312,7 +306,7 @@ 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 ab3e172dcc69..8ee952e7e7d4 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -113,6 +113,7 @@ struct pv_info pv_info = {
#ifdef CONFIG_PARAVIRT_XXL
.extra_user_64bit_cs = __USER_CS,
#endif
+ .io_delay = true,
};
/* 64-bit pagetable entries */
@@ -120,8 +121,6 @@ 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 4806cc28d7ca..a43b525f25cd 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1046,10 +1046,6 @@ 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)
@@ -1209,6 +1205,7 @@ 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",
};
@@ -1253,7 +1250,6 @@ static const typeof(pv_ops) xen_cpu_ops __initconst = {
.invalidate_io_bitmap = xen_invalidate_io_bitmap,
.update_io_bitmap = xen_update_io_bitmap,
#endif
- .io_delay = xen_io_delay,
.start_context_switch = xen_start_context_switch,
.end_context_switch = xen_end_context_switch,
--
2.51.0
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