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Message-ID: <CAKwvOd=bDW6K3PC7S5fiG5n_kwgqhbnVsBHUSGgYaPQY-L_YmA@mail.gmail.com>
Date: Tue, 25 Feb 2020 11:15:54 -0800
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Peter Zijlstra <peterz@...radead.org>,
Wanpeng Li <kernellwp@...il.com>
Subject: Re: [PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per
cpu for both pv tlb and pv ipis
(putting Paolo in To: field, in case email filters are to blame.
Vitaly, maybe you could ping Paolo internally?)
On Mon, Feb 24, 2020 at 11:55 PM Wanpeng Li <kernellwp@...il.com> wrote:
>
> ping,
> On Tue, 18 Feb 2020 at 09:12, Wanpeng Li <kernellwp@...il.com> wrote:
> >
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > 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@...gle.com>
> > Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> > 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");
> > }
> >
> > if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
> > @@ -748,24 +750,31 @@ 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_available() || nopv)
> > return 0;
> >
> > - if (pv_tlb_flush_supported()) {
> > + if (pv_tlb_flush_supported())
> > + alloc = true;
> > +
> > +#if defined(CONFIG_SMP)
> > + if (pv_ipi_supported())
> > + 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
> >
> > --
> > 2.7.4
> >
--
Thanks,
~Nick Desaulniers
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