From: Lance Yang <[email protected]> Enable the optimization introduced in the previous patch for x86.
Add pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast to track whether flush_tlb_multi() sends real IPIs. Initialize it once in native_pv_tlb_init() during boot. On CONFIG_PARAVIRT systems, tlb_table_flush_implies_ipi_broadcast() reads the pv_ops property. On non-PARAVIRT, it directly checks for INVLPGB. PV backends (KVM, Xen, Hyper-V) typically have their own implementations and don't call native_flush_tlb_multi() directly, so they cannot be trusted to provide the IPI guarantees we need. They keep the property false. Two-step plan as David suggested[1]: Step 1 (this patch): Skip redundant sync when we're 100% certain the TLB flush sent IPIs. INVLPGB is excluded because when supported, we cannot guarantee IPIs were sent, keeping it clean and simple. Step 2 (future work): Send targeted IPIs only to CPUs actually doing software/lockless page table walks, benefiting all architectures. Regarding Step 2, it obviously only applies to setups where Step 1 does not apply: like x86 with INVLPGB or arm64. [1] https://lore.kernel.org/linux-mm/[email protected]/ Suggested-by: David Hildenbrand (Arm) <[email protected]> Signed-off-by: Lance Yang <[email protected]> --- arch/x86/include/asm/paravirt_types.h | 5 +++++ arch/x86/include/asm/smp.h | 3 +++ arch/x86/include/asm/tlb.h | 16 +++++++++++++++- arch/x86/include/asm/tlbflush.h | 3 +++ arch/x86/kernel/paravirt.c | 20 ++++++++++++++++++++ arch/x86/kernel/smpboot.c | 1 + arch/x86/mm/tlb.c | 14 ++++++++++++++ 7 files changed, 61 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h index 9bcf6bce88f6..ec01268f2e3e 100644 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -112,6 +112,11 @@ struct pv_mmu_ops { void (*flush_tlb_multi)(const struct cpumask *cpus, const struct flush_tlb_info *info); + /* + * True if flush_tlb_multi() sends real IPIs to all target CPUs. + */ + bool flush_tlb_multi_implies_ipi_broadcast; + /* Hook for intercepting the destruction of an mm_struct. */ void (*exit_mmap)(struct mm_struct *mm); void (*notify_page_enc_status_changed)(unsigned long pfn, int npages, bool enc); diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h index 84951572ab81..ef1fe0cc4c73 100644 --- a/arch/x86/include/asm/smp.h +++ b/arch/x86/include/asm/smp.h @@ -105,6 +105,9 @@ void native_smp_prepare_boot_cpu(void); void smp_prepare_cpus_common(void); void native_smp_prepare_cpus(unsigned int max_cpus); void native_smp_cpus_done(unsigned int max_cpus); + +void __init native_pv_tlb_init(void); + int common_cpu_up(unsigned int cpunum, struct task_struct *tidle); int native_kick_ap(unsigned int cpu, struct task_struct *tidle); int native_cpu_disable(void); diff --git a/arch/x86/include/asm/tlb.h b/arch/x86/include/asm/tlb.h index 866ea78ba156..532578c5a2e7 100644 --- a/arch/x86/include/asm/tlb.h +++ b/arch/x86/include/asm/tlb.h @@ -5,10 +5,19 @@ #define tlb_flush tlb_flush static inline void tlb_flush(struct mmu_gather *tlb); +#define tlb_table_flush_implies_ipi_broadcast tlb_table_flush_implies_ipi_broadcast +static inline bool tlb_table_flush_implies_ipi_broadcast(void); + #include <asm-generic/tlb.h> #include <linux/kernel.h> #include <vdso/bits.h> #include <vdso/page.h> +#include <asm/paravirt.h> + +static inline bool tlb_table_flush_implies_ipi_broadcast(void) +{ + return static_branch_likely(&tlb_ipi_broadcast_key); +} static inline void tlb_flush(struct mmu_gather *tlb) { @@ -20,7 +29,12 @@ static inline void tlb_flush(struct mmu_gather *tlb) end = tlb->end; } - flush_tlb_mm_range(tlb->mm, start, end, stride_shift, tlb->freed_tables); + /* + * Pass both freed_tables and unshared_tables so that lazy-TLB CPUs + * also receive IPIs during unsharing page tables. + */ + flush_tlb_mm_range(tlb->mm, start, end, stride_shift, + tlb->freed_tables || tlb->unshared_tables); } static inline void invlpg(unsigned long addr) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index 5a3cdc439e38..a1b5efef3b90 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -5,6 +5,7 @@ #include <linux/mm_types.h> #include <linux/mmu_notifier.h> #include <linux/sched.h> +#include <linux/jump_label.h> #include <asm/barrier.h> #include <asm/processor.h> @@ -18,6 +19,8 @@ DECLARE_PER_CPU(u64, tlbstate_untag_mask); +DECLARE_STATIC_KEY_FALSE(tlb_ipi_broadcast_key); + void __flush_tlb_all(void); #define TLB_FLUSH_ALL -1UL diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index a6ed52cae003..c8decadf16e0 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -154,6 +154,7 @@ struct paravirt_patch_template pv_ops = { .mmu.flush_tlb_kernel = native_flush_tlb_global, .mmu.flush_tlb_one_user = native_flush_tlb_one_user, .mmu.flush_tlb_multi = native_flush_tlb_multi, + .mmu.flush_tlb_multi_implies_ipi_broadcast = false, .mmu.exit_mmap = paravirt_nop, .mmu.notify_page_enc_status_changed = paravirt_nop, @@ -221,3 +222,22 @@ NOKPROBE_SYMBOL(native_load_idt); EXPORT_SYMBOL(pv_ops); EXPORT_SYMBOL_GPL(pv_info); + +void __init native_pv_tlb_init(void) +{ + /* + * If PV backend already set the property, respect it. + * Otherwise, check if native TLB flush sends real IPIs to all target + * CPUs (i.e., not using INVLPGB broadcast invalidation). + */ + if (pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast) { + static_branch_enable(&tlb_ipi_broadcast_key); + return; + } + + if (pv_ops.mmu.flush_tlb_multi == native_flush_tlb_multi && + !cpu_feature_enabled(X86_FEATURE_INVLPGB)) { + pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast = true; + static_branch_enable(&tlb_ipi_broadcast_key); + } +} diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 5cd6950ab672..3cdb04162843 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1167,6 +1167,7 @@ void __init native_smp_prepare_boot_cpu(void) switch_gdt_and_percpu_base(me); native_pv_lock_init(); + native_pv_tlb_init(); } void __init native_smp_cpus_done(unsigned int max_cpus) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 621e09d049cb..7b1acfb97782 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -26,6 +26,8 @@ #include "mm_internal.h" +DEFINE_STATIC_KEY_FALSE(tlb_ipi_broadcast_key); + #ifdef CONFIG_PARAVIRT # define STATIC_NOPV #else @@ -1834,3 +1836,15 @@ static int __init create_tlb_single_page_flush_ceiling(void) return 0; } late_initcall(create_tlb_single_page_flush_ceiling); + +#ifndef CONFIG_PARAVIRT +void __init native_pv_tlb_init(void) +{ + /* + * For non-PARAVIRT builds, check if native TLB flush sends real IPIs + * (i.e., not using INVLPGB broadcast invalidation). + */ + if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) + static_branch_enable(&tlb_ipi_broadcast_key); +} +#endif -- 2.49.0
