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Peter Anvin" , Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Paolo Bonzini , Vitaly Kuznetsov , Boris Ostrovsky , xen-devel@lists.xenproject.org Subject: [PATCH v4 2/6] x86/paravirt: Replace io_delay() hook with a bool Date: Mon, 19 Jan 2026 19:26:28 +0100 Message-ID: <20260119182632.596369-3-jgross@suse.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260119182632.596369-1-jgross@suse.com> References: <20260119182632.596369-1-jgross@suse.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.com:s=susede1]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FUZZY_RATELIMITED(0.00)[rspamd.com]; ARC_NA(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; MIME_TRACE(0.00)[0:+]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; RCPT_COUNT_TWELVE(0.00)[17]; RCVD_COUNT_TWO(0.00)[2]; URIBL_BLOCKED(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.com:mid,suse.com:dkim,suse.com:email]; TO_MATCH_ENVRCPT_ALL(0.00)[]; R_RATELIMIT(0.00)[to_ip_from(RLkdkdrsxe9hqhhs5ask8616i6)]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; DKIM_TRACE(0.00)[suse.com:+]; FROM_HAS_DN(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:mid,suse.com:dkim,suse.com:email] X-Spam-Flag: NO X-Spam-Score: -3.01 X-Rspamd-Queue-Id: 7F8025BCCF X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spam-Level: X-ZohoMail-DKIM: pass (identity @suse.com) X-ZM-MESSAGEID: 1768847244378154100 Content-Type: text/plain; charset="utf-8" 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 --- 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); =20 #if defined(CONFIG_PARAVIRT) -#include +#include #else +#define call_io_delay() true +#endif =20 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 } =20 -#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/pa= ravirt-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; }; =20 @@ -26,6 +28,10 @@ u64 _paravirt_ident_64(u64); #endif #define paravirt_nop ((void *)nop_func) =20 +#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/paravir= t.h index b21072af731d..f4885bd98a18 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -19,17 +19,6 @@ #include #include =20 -/* 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/p= aravirt_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 { =20 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 =3D "VMware hypervisor"; - pv_ops.cpu.io_delay =3D paravirt_nop; + pv_info.io_delay =3D false; =20 if (vmware_tsc_khz =3D=3D 0) return; diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 26ab6f8e36df..911950c9110c 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_ti= me) __aligned(64) __visi static int has_steal_clock =3D 0; =20 static int has_guest_poll =3D 0; -/* - * No need for any "IO delay" on KVM - */ -static void kvm_io_delay(void) -{ -} =20 #define KVM_TASK_SLEEP_HASHBITS 8 #define KVM_TASK_SLEEP_HASHSIZE (1<