From: Borislav Petkov (AMD) Date: Thu, 3 Apr 2025 08:56:23 +0000 (+0200) Subject: x86/tlb: Simplify choose_new_asid() and generate better code X-Git-Tag: v6.16-rc1~195^2~26^2~14 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2fb34b1566a386913b291d04f91ba6f6e6a5bb99;p=thirdparty%2Flinux.git x86/tlb: Simplify choose_new_asid() and generate better code Have it return the two things it does return: - a new ASID and - the need to flush the TLB or not, in a struct which fits in a single 32-bit register and whack the IO parameters. Beyond being easier to read, this also helps the compiler generate better, more compact code: # arch/x86/mm/tlb.o: text data bss dec hex filename 9341 753 516 10610 2972 tlb.o.before 9213 753 516 10482 28f2 tlb.o.after No functional changes. Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Brian Gerst Cc: Juergen Gross Cc: Andrew Cooper Cc: Uros Bizjak Cc: Rik van Riel Cc: "H. Peter Anvin" Cc: Peter Zijlstra Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250403085623.20824-1-bp@kernel.org --- diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index e459d97ef3977..d00ae21d0ee26 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -215,16 +215,20 @@ static void clear_asid_other(void) atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1); +struct new_asid { + unsigned int asid : 16; + unsigned int need_flush : 1; +}; -static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen, - u16 *new_asid, bool *need_flush) +static struct new_asid choose_new_asid(struct mm_struct *next, u64 next_tlb_gen) { + struct new_asid ns; u16 asid; if (!static_cpu_has(X86_FEATURE_PCID)) { - *new_asid = 0; - *need_flush = true; - return; + ns.asid = 0; + ns.need_flush = 1; + return ns; } /* @@ -235,9 +239,9 @@ static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen, u16 global_asid = mm_global_asid(next); if (global_asid) { - *new_asid = global_asid; - *need_flush = false; - return; + ns.asid = global_asid; + ns.need_flush = 0; + return ns; } } @@ -249,22 +253,23 @@ static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen, next->context.ctx_id) continue; - *new_asid = asid; - *need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) < - next_tlb_gen); - return; + ns.asid = asid; + ns.need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) < next_tlb_gen); + return ns; } /* * We don't currently own an ASID slot on this CPU. * Allocate a slot. */ - *new_asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1; - if (*new_asid >= TLB_NR_DYN_ASIDS) { - *new_asid = 0; + ns.asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1; + if (ns.asid >= TLB_NR_DYN_ASIDS) { + ns.asid = 0; this_cpu_write(cpu_tlbstate.next_asid, 1); } - *need_flush = true; + ns.need_flush = true; + + return ns; } /* @@ -781,9 +786,9 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, bool was_lazy = this_cpu_read(cpu_tlbstate_shared.is_lazy); unsigned cpu = smp_processor_id(); unsigned long new_lam; + struct new_asid ns; u64 next_tlb_gen; - bool need_flush; - u16 new_asid; + /* We don't want flush_tlb_func() to run concurrently with us. */ if (IS_ENABLED(CONFIG_PROVE_LOCKING)) @@ -854,7 +859,7 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, /* Check if the current mm is transitioning to a global ASID */ if (mm_needs_global_asid(next, prev_asid)) { next_tlb_gen = atomic64_read(&next->context.tlb_gen); - choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush); + ns = choose_new_asid(next, next_tlb_gen); goto reload_tlb; } @@ -889,8 +894,8 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, * TLB contents went out of date while we were in lazy * mode. Fall through to the TLB switching code below. */ - new_asid = prev_asid; - need_flush = true; + ns.asid = prev_asid; + ns.need_flush = true; } else { /* * Apply process to process speculation vulnerability @@ -918,21 +923,21 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, cpumask_set_cpu(cpu, mm_cpumask(next)); next_tlb_gen = atomic64_read(&next->context.tlb_gen); - choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush); + ns = choose_new_asid(next, next_tlb_gen); } reload_tlb: new_lam = mm_lam_cr3_mask(next); - if (need_flush) { - VM_WARN_ON_ONCE(is_global_asid(new_asid)); - this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id); - this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen); - load_new_mm_cr3(next->pgd, new_asid, new_lam, true); + if (ns.need_flush) { + VM_WARN_ON_ONCE(is_global_asid(ns.asid)); + this_cpu_write(cpu_tlbstate.ctxs[ns.asid].ctx_id, next->context.ctx_id); + this_cpu_write(cpu_tlbstate.ctxs[ns.asid].tlb_gen, next_tlb_gen); + load_new_mm_cr3(next->pgd, ns.asid, new_lam, true); trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); } else { /* The new ASID is already up to date. */ - load_new_mm_cr3(next->pgd, new_asid, new_lam, false); + load_new_mm_cr3(next->pgd, ns.asid, new_lam, false); trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, 0); } @@ -941,7 +946,7 @@ reload_tlb: barrier(); this_cpu_write(cpu_tlbstate.loaded_mm, next); - this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid); + this_cpu_write(cpu_tlbstate.loaded_mm_asid, ns.asid); cpu_tlbstate_update_lam(new_lam, mm_untag_mask(next)); if (next != prev) {