Wanpeng Li <kernellwp@xxxxxxxxx> writes: > On Mon, 17 Feb 2020 at 20:46, 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> >> > --- >> > v1 -> v2: >> > * remove '!alloc' check >> > * use new pv check helpers >> > >> > 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 76ea8c4..377b224 100644 >> > --- a/arch/x86/kernel/kvm.c >> > +++ b/arch/x86/kernel/kvm.c >> > @@ -432,6 +432,8 @@ static bool pv_tlb_flush_supported(void) >> > kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)); >> > } >> > >> > +static DEFINE_PER_CPU(cpumask_var_t, __pv_cpu_mask); >> > + >> > #ifdef CONFIG_SMP >> > >> > static bool pv_ipi_supported(void) >> > @@ -510,12 +512,12 @@ 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); >> > } >> > >> > @@ -595,7 +597,6 @@ 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) >> > @@ -603,7 +604,7 @@ 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); >> > /* >> > @@ -642,6 +643,7 @@ static void __init kvm_guest_init(void) >> > if (pv_tlb_flush_supported()) { >> > 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"); >> >> Nit: to be consistent with __send_ipi_mask() the message should be >> somthing like >> >> "KVM: switch to using PV TLB flush" > > There is a lot of native ops we replace by pv ops in kvm.c, I use "KVM > setup xxx" there, like pv ipis, pv tlb flush, pv sched yield, should > we keep consistent as before? > Oh, I see, it's either one or another :-) Personally, I prefer when subsystem is delimited with ':' so if we were to change them all I'd prefer the "KVM: switch to using PV TLB flush" (__send_ipi_mask() style). But this looks more like a separate patch idea, we can discuss our personal preferences there :-) -- Vitaly
