From dc98e3bd494bef9c8933ee9ace254aac48efe506 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 9 Jul 2025 09:02:10 +0530 Subject: [PATCH] x86/apic: KVM: Deduplicate APIC vector => register+bit math Consolidate KVM's {REG,VEC}_POS() macros and lapic_vector_set_in_irr()'s open coded equivalent logic in anticipation of the kernel gaining more usage of vector => reg+bit lookups. Use lapic_vector_set_in_irr()'s math as using divides for both the bit number and register offset makes it easier to connect the dots, and for at least one user, fixup_irqs(), "/ 32 * 0x10" generates ever so slightly better code with gcc-14 (shaves a whole 3 bytes from the code stream): ((v) >> 5) << 4: c1 ef 05 shr $0x5,%edi c1 e7 04 shl $0x4,%edi 81 c7 00 02 00 00 add $0x200,%edi (v) / 32 * 0x10: c1 ef 05 shr $0x5,%edi 83 c7 20 add $0x20,%edi c1 e7 04 shl $0x4,%edi Keep KVM's tersely named macros as "wrappers" to avoid unnecessary churn in KVM, and because the shorter names yield more readable code overall in KVM. The new macros type cast the vector parameter to "unsigned int". This is required from better code generation for cases where an "int" is passed to these macros in KVM code. int v; ((v) >> 5) << 4: c1 f8 05 sar $0x5,%eax c1 e0 04 shl $0x4,%eax ((v) / 32 * 0x10): 85 ff test %edi,%edi 8d 47 1f lea 0x1f(%rdi),%eax 0f 49 c7 cmovns %edi,%eax c1 f8 05 sar $0x5,%eax c1 e0 04 shl $0x4,%eax ((unsigned int)(v) / 32 * 0x10): c1 f8 05 sar $0x5,%eax c1 e0 04 shl $0x4,%eax (v) & (32 - 1): 89 f8 mov %edi,%eax 83 e0 1f and $0x1f,%eax (v) % 32 89 fa mov %edi,%edx c1 fa 1f sar $0x1f,%edx c1 ea 1b shr $0x1b,%edx 8d 04 17 lea (%rdi,%rdx,1),%eax 83 e0 1f and $0x1f,%eax 29 d0 sub %edx,%eax (unsigned int)(v) % 32: 89 f8 mov %edi,%eax 83 e0 1f and $0x1f,%eax Overall kvm.ko text size is impacted if "unsigned int" is not used. Bin Orig New (w/o unsigned int) New (w/ unsigned int) lapic.o 28580 28772 28580 kvm.o 670810 671002 670810 kvm.ko 708079 708271 708079 No functional change intended. [Neeraj: Type cast vec macro param to "unsigned int", provide data in commit log on "unsigned int" requirement] Signed-off-by: Neeraj Upadhyay Link: https://lore.kernel.org/r/20250709033242.267892-4-Neeraj.Upadhyay@amd.com Signed-off-by: Sean Christopherson --- arch/x86/include/asm/apic.h | 7 +++++-- arch/x86/kvm/lapic.h | 4 ++-- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h index 23d86c9750b9f..c84d4e86fe4ed 100644 --- a/arch/x86/include/asm/apic.h +++ b/arch/x86/include/asm/apic.h @@ -488,11 +488,14 @@ static inline void apic_setup_apic_calls(void) { } extern void apic_ack_irq(struct irq_data *data); +#define APIC_VECTOR_TO_BIT_NUMBER(v) ((unsigned int)(v) % 32) +#define APIC_VECTOR_TO_REG_OFFSET(v) ((unsigned int)(v) / 32 * 0x10) + static inline bool lapic_vector_set_in_irr(unsigned int vector) { - u32 irr = apic_read(APIC_IRR + (vector / 32 * 0x10)); + u32 irr = apic_read(APIC_IRR + APIC_VECTOR_TO_REG_OFFSET(vector)); - return !!(irr & (1U << (vector % 32))); + return !!(irr & (1U << APIC_VECTOR_TO_BIT_NUMBER(vector))); } static inline bool is_vector_pending(unsigned int vector) diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h index 1638a3da383a8..56369d331bfc7 100644 --- a/arch/x86/kvm/lapic.h +++ b/arch/x86/kvm/lapic.h @@ -145,8 +145,8 @@ void kvm_lapic_exit(void); u64 kvm_lapic_readable_reg_mask(struct kvm_lapic *apic); -#define VEC_POS(v) ((v) & (32 - 1)) -#define REG_POS(v) (((v) >> 5) << 4) +#define VEC_POS(v) APIC_VECTOR_TO_BIT_NUMBER(v) +#define REG_POS(v) APIC_VECTOR_TO_REG_OFFSET(v) static inline void kvm_lapic_clear_vector(int vec, void *bitmap) { -- 2.47.2