From: Lance Yang <[email protected]> When the TLB flush path already sends IPIs (e.g. native without INVLPGB, or KVM), tlb_remove_table_sync_mm() does not need to send another round.
Add a property on pv_mmu_ops so each paravirt backend can indicate whether its flush_tlb_multi sends real IPIs; if so, tlb_remove_table_sync_mm() is a no-op. Native sets it in native_pv_tlb_init() when still using native_flush_tlb_multi() and INVLPGB is disabled. KVM sets it true; Xen and Hyper-V set it false because they use hypercalls. Also pass both freed_tables and unshared_tables from tlb_flush() into flush_tlb_mm_range() so lazy-TLB CPUs get IPIs during hugetlb unshare. Suggested-by: David Hildenbrand (Red Hat) <[email protected]> Signed-off-by: Lance Yang <[email protected]> --- arch/x86/hyperv/mmu.c | 5 +++++ arch/x86/include/asm/paravirt.h | 5 +++++ arch/x86/include/asm/paravirt_types.h | 6 ++++++ arch/x86/include/asm/tlb.h | 20 +++++++++++++++++++- arch/x86/kernel/kvm.c | 6 ++++++ arch/x86/kernel/paravirt.c | 18 ++++++++++++++++++ arch/x86/kernel/smpboot.c | 1 + arch/x86/xen/mmu_pv.c | 2 ++ include/asm-generic/tlb.h | 15 +++++++++++++++ mm/mmu_gather.c | 7 +++++++ 10 files changed, 84 insertions(+), 1 deletion(-) diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c index cfcb60468b01..fc8fb275f295 100644 --- a/arch/x86/hyperv/mmu.c +++ b/arch/x86/hyperv/mmu.c @@ -243,4 +243,9 @@ void hyperv_setup_mmu_ops(void) pr_info("Using hypercall for remote TLB flush\n"); pv_ops.mmu.flush_tlb_multi = hyperv_flush_tlb_multi; + /* + * Hyper-V uses hypercalls for TLB flush, not real IPIs. + * Keep the property as false. + */ + pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast = false; } diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h index 13f9cd31c8f8..1fdbe3736f41 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -698,6 +698,7 @@ static __always_inline unsigned long arch_local_irq_save(void) extern void default_banner(void); void native_pv_lock_init(void) __init; +void native_pv_tlb_init(void) __init; #else /* __ASSEMBLER__ */ @@ -727,6 +728,10 @@ void native_pv_lock_init(void) __init; static inline void native_pv_lock_init(void) { } + +static inline void native_pv_tlb_init(void) +{ +} #endif #endif /* !CONFIG_PARAVIRT */ diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h index 3502939415ad..d8aa519ef5e3 100644 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -133,6 +133,12 @@ struct pv_mmu_ops { void (*flush_tlb_multi)(const struct cpumask *cpus, const struct flush_tlb_info *info); + /* + * Indicates whether flush_tlb_multi IPIs provide sufficient + * synchronization during TLB flush when freeing or unsharing page tables. + */ + 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/tlb.h b/arch/x86/include/asm/tlb.h index 866ea78ba156..1e524d8e260a 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); + /* + * During TLB flushes, pass both freed_tables and unshared_tables + * so lazy-TLB CPUs receive IPIs. + */ + 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/kvm.c b/arch/x86/kernel/kvm.c index 37dc8465e0f5..6a5e47ee4eb6 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -856,6 +856,12 @@ static void __init kvm_guest_init(void) #ifdef CONFIG_SMP if (pv_tlb_flush_supported()) { pv_ops.mmu.flush_tlb_multi = kvm_flush_tlb_multi; + /* + * KVM's flush implementation calls native_flush_tlb_multi(), + * which sends real IPIs when INVLPGB is not available. + */ + if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) + pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast = true; pr_info("KVM setup pv remote TLB flush\n"); } diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index ab3e172dcc69..1af253c9f51d 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -60,6 +60,23 @@ void __init native_pv_lock_init(void) static_branch_enable(&virt_spin_lock_key); } +void __init native_pv_tlb_init(void) +{ + /* + * Check if we're still using native TLB flush (not overridden by + * a PV backend) and don't have INVLPGB support. + * + * In this case, native IPI-based TLB flush provides sufficient + * synchronization for GUP-fast. + * + * PV backends (KVM, Xen, HyperV) should set this property in their + * own initialization code if their flush implementation sends IPIs. + */ + 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; +} + struct static_key paravirt_steal_enabled; struct static_key paravirt_steal_rq_enabled; @@ -173,6 +190,7 @@ 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, 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/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c index 7a35c3393df4..b6d86299cf10 100644 --- a/arch/x86/xen/mmu_pv.c +++ b/arch/x86/xen/mmu_pv.c @@ -2185,6 +2185,8 @@ static const typeof(pv_ops) xen_mmu_ops __initconst = { .flush_tlb_kernel = xen_flush_tlb, .flush_tlb_one_user = xen_flush_tlb_one_user, .flush_tlb_multi = xen_flush_tlb_multi, + /* Xen uses hypercalls for TLB flush, not real IPIs */ + .flush_tlb_multi_implies_ipi_broadcast = false, .pgd_alloc = xen_pgd_alloc, .pgd_free = xen_pgd_free, diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index 40eb74b28f9d..fae97c8bcceb 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -240,6 +240,21 @@ static inline void tlb_remove_table(struct mmu_gather *tlb, void *table) } #endif /* CONFIG_MMU_GATHER_TABLE_FREE */ +/* + * Architectures can override this to indicate whether TLB flush operations + * send IPIs that are sufficient to synchronize with lockless page table + * walkers (e.g., GUP-fast). If true, tlb_remove_table_sync_mm() becomes + * a no-op as the TLB flush already provided the necessary IPI. + * + * Default is false, meaning we need explicit IPIs via tlb_remove_table_sync_mm(). + */ +#ifndef tlb_table_flush_implies_ipi_broadcast +static inline bool tlb_table_flush_implies_ipi_broadcast(void) +{ + return false; +} +#endif + #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE /* * This allows an architecture that does not use the linux page-tables for diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index 76573ec454e5..9620480c11ce 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -303,6 +303,13 @@ void tlb_remove_table_sync_mm(struct mm_struct *mm) bool found_any = false; int cpu; + /* + * If the architecture's TLB flush already sent IPIs that are sufficient + * for synchronization, we don't need to send additional IPIs. + */ + if (tlb_table_flush_implies_ipi_broadcast()) + return; + if (WARN_ONCE(!mm, "NULL mm in %s\n", __func__)) { tlb_remove_table_sync_one(); return; -- 2.49.0
