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Message-ID: <20260115084849.31502-2-jgross@suse.com>
Date: Thu, 15 Jan 2026 09:48:45 +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@...nel.org>,
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 v3 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>
---
V3:
- rebase to tip/master kernel branch
---
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 ca309a3227c7..8a9292ce7d2d 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -243,11 +243,16 @@ 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();
@@ -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-base.h b/arch/x86/include/asm/paravirt-base.h
index 982a0b93bc76..3b9e7772d196 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 b21072af731d..f4885bd98a18 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 7ccd41628d36..3946d0f69921 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 a3e6936839b1..eee0d1a48802 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 de550b12d9ab..8c3221048d9f 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)
@@ -314,7 +308,7 @@ 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 a6ed52cae003..792fa96b3233 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 8a19a88190ee..9c9695f5d158 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",
};
@@ -1392,7 +1389,6 @@ 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;
--
2.51.0
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