From: Rik van Riel <riel@xxxxxxxxxxx> Add functions to manage global ASID space. Multithreaded processes that are simultaneously active on 4 or more CPUs can get a global ASID, resulting in the same PCID being used for that process on every CPU. This in turn will allow the kernel to use hardware-assisted TLB flushing through AMD INVLPGB or Intel RAR for these processes. [ bp: - Extend use_global_asid() comment - s/X86_BROADCAST_TLB_FLUSH/BROADCAST_TLB_FLUSH/g - other touchups ] Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx> Link: https://lore.kernel.org/r/20250226030129.530345-8-riel@xxxxxxxxxxx --- arch/x86/include/asm/mmu.h | 12 +++ arch/x86/include/asm/mmu_context.h | 2 + arch/x86/include/asm/tlbflush.h | 37 +++++++ arch/x86/mm/tlb.c | 154 ++++++++++++++++++++++++++++- 4 files changed, 202 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h index 3b496cdcb74b..8b8055a8eb9e 100644 --- a/arch/x86/include/asm/mmu.h +++ b/arch/x86/include/asm/mmu.h @@ -69,6 +69,18 @@ typedef struct { u16 pkey_allocation_map; s16 execute_only_pkey; #endif + +#ifdef CONFIG_BROADCAST_TLB_FLUSH + /* + * The global ASID will be a non-zero value when the process has + * the same ASID across all CPUs, allowing it to make use of + * hardware-assisted remote TLB invalidation like AMD INVLPGB. + */ + u16 global_asid; + + /* The process is transitioning to a new global ASID number. */ + bool asid_transition; +#endif } mm_context_t; #define INIT_MM_CONTEXT(mm) \ diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 795fdd53bd0a..a2c70e495b1b 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -139,6 +139,8 @@ static inline void mm_reset_untag_mask(struct mm_struct *mm) #define enter_lazy_tlb enter_lazy_tlb extern void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk); +extern void mm_free_global_asid(struct mm_struct *mm); + /* * Init a new mm. Used on mm copies, like at fork() * and on mm's that are brand-new, like at execve(). diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index 855c13da2045..f7b374bcdc0b 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -6,6 +6,7 @@ #include <linux/mmu_notifier.h> #include <linux/sched.h> +#include <asm/barrier.h> #include <asm/processor.h> #include <asm/cpufeature.h> #include <asm/special_insns.h> @@ -234,6 +235,42 @@ void flush_tlb_one_kernel(unsigned long addr); void flush_tlb_multi(const struct cpumask *cpumask, const struct flush_tlb_info *info); +static inline bool is_dyn_asid(u16 asid) +{ + return asid < TLB_NR_DYN_ASIDS; +} + +#ifdef CONFIG_BROADCAST_TLB_FLUSH +static inline u16 mm_global_asid(struct mm_struct *mm) +{ + u16 asid; + + if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) + return 0; + + asid = smp_load_acquire(&mm->context.global_asid); + + /* mm->context.global_asid is either 0, or a global ASID */ + VM_WARN_ON_ONCE(asid && is_dyn_asid(asid)); + + return asid; +} + +static inline void mm_assign_global_asid(struct mm_struct *mm, u16 asid) +{ + /* + * Notably flush_tlb_mm_range() -> broadcast_tlb_flush() -> + * finish_asid_transition() needs to observe asid_transition = true + * once it observes global_asid. + */ + mm->context.asid_transition = true; + smp_store_release(&mm->context.global_asid, asid); +} +#else +static inline u16 mm_global_asid(struct mm_struct *mm) { return 0; } +static inline void mm_assign_global_asid(struct mm_struct *mm, u16 asid) { } +#endif /* CONFIG_BROADCAST_TLB_FLUSH */ + #ifdef CONFIG_PARAVIRT #include <asm/paravirt.h> #endif diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 76b4a88afb56..6c24d967b77d 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -74,13 +74,15 @@ * use different names for each of them: * * ASID - [0, TLB_NR_DYN_ASIDS-1] - * the canonical identifier for an mm + * the canonical identifier for an mm, dynamically allocated on each CPU + * [TLB_NR_DYN_ASIDS, MAX_ASID_AVAILABLE-1] + * the canonical, global identifier for an mm, identical across all CPUs * - * kPCID - [1, TLB_NR_DYN_ASIDS] + * kPCID - [1, MAX_ASID_AVAILABLE] * the value we write into the PCID part of CR3; corresponds to the * ASID+1, because PCID 0 is special. * - * uPCID - [2048 + 1, 2048 + TLB_NR_DYN_ASIDS] + * uPCID - [2048 + 1, 2048 + MAX_ASID_AVAILABLE] * for KPTI each mm has two address spaces and thus needs two * PCID values, but we can still do with a single ASID denomination * for each mm. Corresponds to kPCID + 2048. @@ -251,6 +253,152 @@ static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen, *need_flush = true; } +/* + * Global ASIDs are allocated for multi-threaded processes that are + * active on multiple CPUs simultaneously, giving each of those + * processes the same PCID on every CPU, for use with hardware-assisted + * TLB shootdown on remote CPUs, like AMD INVLPGB or Intel RAR. + * + * These global ASIDs are held for the lifetime of the process. + */ +static DEFINE_RAW_SPINLOCK(global_asid_lock); +static u16 last_global_asid = MAX_ASID_AVAILABLE; +static DECLARE_BITMAP(global_asid_used, MAX_ASID_AVAILABLE); +static DECLARE_BITMAP(global_asid_freed, MAX_ASID_AVAILABLE); +static int global_asid_available = MAX_ASID_AVAILABLE - TLB_NR_DYN_ASIDS - 1; + +/* + * When the search for a free ASID in the global ASID space reaches + * MAX_ASID_AVAILABLE, a global TLB flush guarantees that previously + * freed global ASIDs are safe to re-use. + * + * This way the global flush only needs to happen at ASID rollover + * time, and not at ASID allocation time. + */ +static void reset_global_asid_space(void) +{ + lockdep_assert_held(&global_asid_lock); + + invlpgb_flush_all_nonglobals(); + + /* + * The TLB flush above makes it safe to re-use the previously + * freed global ASIDs. + */ + bitmap_andnot(global_asid_used, global_asid_used, + global_asid_freed, MAX_ASID_AVAILABLE); + bitmap_clear(global_asid_freed, 0, MAX_ASID_AVAILABLE); + + /* Restart the search from the start of global ASID space. */ + last_global_asid = TLB_NR_DYN_ASIDS; +} + +static u16 allocate_global_asid(void) +{ + u16 asid; + + lockdep_assert_held(&global_asid_lock); + + /* The previous allocation hit the edge of available address space */ + if (last_global_asid >= MAX_ASID_AVAILABLE - 1) + reset_global_asid_space(); + + asid = find_next_zero_bit(global_asid_used, MAX_ASID_AVAILABLE, last_global_asid); + + if (asid >= MAX_ASID_AVAILABLE && !global_asid_available) { + /* This should never happen. */ + VM_WARN_ONCE(1, "Unable to allocate global ASID despite %d available\n", + global_asid_available); + return 0; + } + + /* Claim this global ASID. */ + __set_bit(asid, global_asid_used); + last_global_asid = asid; + global_asid_available--; + return asid; +} + +/* + * Check whether a process is currently active on more than @threshold CPUs. + * This is a cheap estimation on whether or not it may make sense to assign + * a global ASID to this process, and use broadcast TLB invalidation. + */ +static bool mm_active_cpus_exceeds(struct mm_struct *mm, int threshold) +{ + int count = 0; + int cpu; + + /* This quick check should eliminate most single threaded programs. */ + if (cpumask_weight(mm_cpumask(mm)) <= threshold) + return false; + + /* Slower check to make sure. */ + for_each_cpu(cpu, mm_cpumask(mm)) { + /* Skip the CPUs that aren't really running this process. */ + if (per_cpu(cpu_tlbstate.loaded_mm, cpu) != mm) + continue; + + if (per_cpu(cpu_tlbstate_shared.is_lazy, cpu)) + continue; + + if (++count > threshold) + return true; + } + return false; +} + +/* + * Assign a global ASID to the current process, protecting against + * races between multiple threads in the process. + */ +static void use_global_asid(struct mm_struct *mm) +{ + u16 asid; + + guard(raw_spinlock_irqsave)(&global_asid_lock); + + /* This process is already using broadcast TLB invalidation. */ + if (mm_global_asid(mm)) + return; + + /* + * The last global ASID was consumed while waiting for the lock. + * + * If this fires, a more aggressive ASID reuse scheme might be + * needed. + */ + if (!global_asid_available) { + VM_WARN_ONCE(1, "Ran out of global ASIDs\n"); + return; + } + + asid = allocate_global_asid(); + if (!asid) + return; + + mm_assign_global_asid(mm, asid); +} + +void mm_free_global_asid(struct mm_struct *mm) +{ + if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) + return; + + if (!mm_global_asid(mm)) + return; + + guard(raw_spinlock_irqsave)(&global_asid_lock); + + /* The global ASID can be re-used only after flush at wrap-around. */ +#ifdef CONFIG_BROADCAST_TLB_FLUSH + __set_bit(mm->context.global_asid, global_asid_freed); + + mm->context.global_asid = 0; + global_asid_available++; +#endif +} + /* * Given an ASID, flush the corresponding user ASID. We can delay this * until the next time we switch to it. -- 2.43.0
