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 | 7 +++++++ arch/x86/include/asm/tlb.h | 20 +++++++++++++++++++- arch/x86/kernel/paravirt.c | 16 ++++++++++++++++ arch/x86/kernel/smpboot.c | 1 + 5 files changed, 48 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..4ac175414ac1 100644 --- a/arch/x86/include/asm/smp.h +++ b/arch/x86/include/asm/smp.h @@ -105,6 +105,13 @@ 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); + +#ifdef CONFIG_PARAVIRT +void __init native_pv_tlb_init(void); +#else +static inline void native_pv_tlb_init(void) { } +#endif + 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..87ef7147eac8 100644 --- a/arch/x86/include/asm/tlb.h +++ b/arch/x86/include/asm/tlb.h @@ -5,10 +5,23 @@ #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) +{ +#ifdef CONFIG_PARAVIRT + return pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast; +#else + return !cpu_feature_enabled(X86_FEATURE_INVLPGB); +#endif +} static inline void tlb_flush(struct mmu_gather *tlb) { @@ -20,7 +33,12 @@ 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/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index a6ed52cae003..b681b8319295 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 +222,18 @@ 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) + 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; +} 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) -- 2.49.0
