Commit 8a9442f4 authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
Browse files

KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis 

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: default avatarNick Desaulniers <ndesaulniers@google.com>
Acked-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Reviewed-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarWanpeng Li <wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a262bca3

arch/x86/kernel/kvm.c

+21 −12
Original line number Diff line number Diff line
@@ -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

CRA Git | Maintained and supported by SUSTech CRA and CCSE