Cc Thadeu, On Tue, 4 Feb 2020 at 20:57, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote: > > Wanpeng Li <kernellwp@xxxxxxxxx> writes: > > > From: Wanpeng Li <wanpengli@xxxxxxxxxxx> > > > > Nick Desaulniers Reported: > > > > 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. > > > > This patch fixes it by pre-allocate 1 cpumask variable per cpu and use it for > > both pv tlb and pv ipis.. > > > > Reported-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > 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); > > 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' check is superfluous. > > > + 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); > > Honestly, I'd simplify the check in kvm_alloc_cpumask() as > > if (!kvm_para_available()) > return; > > and allocated masks for all other cases. This will waste the memory if pv tlb and pv ipis are not exposed which are the only users currently. Wanpeng
