On Mon, Feb 3, 2020 at 8:32 AM Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > > Hi Nick, > On Mon, 27 Jan 2020 at 15:16, Nick Desaulniers > <nick.desaulniers@xxxxxxxxx> wrote: > > > > This helps avoid avoid a potentially large stack allocation. > > > > When building with: > > $ make CC=clang arch/x86/ CFLAGS=-Wframe-larger-than=1000 > > The following warning is observed: > > arch/x86/kernel/kvm.c:494:13: warning: stack frame size of 1064 bytes in > > function 'kvm_send_ipi_mask_allbutself' [-Wframe-larger-than=] > > static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, int > > vector) > > ^ > > Debugging with: > > https://github.com/ClangBuiltLinux/frame-larger-than > > via: > > $ python3 frame_larger_than.py arch/x86/kernel/kvm.o \ > > kvm_send_ipi_mask_allbutself > > points to the stack allocated `struct cpumask newmask` in > > `kvm_send_ipi_mask_allbutself`. The size of a `struct cpumask` is > > potentially large, as it's CONFIG_NR_CPUS divided by BITS_PER_LONG for > > the target architecture. CONFIG_NR_CPUS for X86_64 can be as high as > > 8192, making a single instance of a `struct cpumask` 1024 B. > > Could you help test the below untested patch? > > From 867753e2fa27906f15df7902ba1bce7f9cef6ebe Mon Sep 17 00:00:00 2001 > From: Wanpeng Li <wanpengli@xxxxxxxxxxx> > Date: Mon, 3 Feb 2020 16:26:35 +0800 > Subject: [PATCH] KVM: Pre-allocate 1 cpumask variable per cpu for both > pv tlb and pv ipis > > Reported-by: Nick Desaulniers <nick.desaulniers@xxxxxxxxx> > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> > --- > arch/x86/kernel/kvm.c | 33 +++++++++++++++++++++------------ > 1 file changed, 21 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 81045aab..b1e8efa 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -425,6 +425,8 @@ static void __init sev_map_percpu_data(void) > } > } > > +static DEFINE_PER_CPU(cpumask_var_t, __pv_cpu_mask); > + > #ifdef CONFIG_SMP > #define KVM_IPI_CLUSTER_SIZE (2 * BITS_PER_LONG) > > @@ -490,12 +492,12 @@ static void kvm_send_ipi_mask(const struct > cpumask *mask, int vector) > static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, > int vector) > { > unsigned int this_cpu = smp_processor_id(); > - struct cpumask new_mask; > + struct cpumask *new_mask = this_cpu_cpumask_var_ptr(__pv_cpu_mask); Yes, this should help reduce the stack usage, thanks. Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > const struct cpumask *local_mask; > > - cpumask_copy(&new_mask, mask); > - cpumask_clear_cpu(this_cpu, &new_mask); > - local_mask = &new_mask; > + cpumask_copy(new_mask, mask); > + cpumask_clear_cpu(this_cpu, new_mask); > + local_mask = new_mask; > __send_ipi_mask(local_mask, vector); > } > > @@ -575,7 +577,6 @@ static void __init kvm_apf_trap_init(void) > update_intr_gate(X86_TRAP_PF, async_page_fault); > } > > -static DEFINE_PER_CPU(cpumask_var_t, __pv_tlb_mask); > > static void kvm_flush_tlb_others(const struct cpumask *cpumask, > const struct flush_tlb_info *info) > @@ -583,7 +584,7 @@ static void kvm_flush_tlb_others(const struct > cpumask *cpumask, > u8 state; > int cpu; > struct kvm_steal_time *src; > - struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_tlb_mask); > + struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask); > > cpumask_copy(flushmask, cpumask); > /* > @@ -624,6 +625,7 @@ static void __init kvm_guest_init(void) > kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { > pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others; > pv_ops.mmu.tlb_remove_table = tlb_remove_table; > + pr_info("KVM setup pv remote TLB flush\n"); > } > > if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) > @@ -732,23 +734,30 @@ static __init int activate_jump_labels(void) > } > arch_initcall(activate_jump_labels); > > -static __init int kvm_setup_pv_tlb_flush(void) > +static __init int kvm_alloc_cpumask(void) > { > int cpu; > + bool alloc = false; > > if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && > !kvm_para_has_hint(KVM_HINTS_REALTIME) && > - kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { > + kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) > + alloc = true; > + > +#if defined(CONFIG_SMP) > + if (!alloc && kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI)) > + alloc = true; > +#endif > + > + if (alloc) > for_each_possible_cpu(cpu) { > - zalloc_cpumask_var_node(per_cpu_ptr(&__pv_tlb_mask, cpu), > + zalloc_cpumask_var_node(per_cpu_ptr(&__pv_cpu_mask, cpu), > GFP_KERNEL, cpu_to_node(cpu)); > } > - pr_info("KVM setup pv remote TLB flush\n"); > - } > > return 0; > } > -arch_initcall(kvm_setup_pv_tlb_flush); > +arch_initcall(kvm_alloc_cpumask); > > #ifdef CONFIG_PARAVIRT_SPINLOCKS > > -- > 1.8.3.1 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CANRm%2BCwK0Cg45mktda9Yz9fsjPCvtuB8O%2Bfma5L3tV725ki1qw%40mail.gmail.com. -- Thanks, ~Nick Desaulniers
