[PATCH RESEND v2 1/2] KVM: Introduce pv check helpers

[PATCH RESEND v2 1/2] KVM: Introduce pv check helpers

[Wanpeng Li]

From: Wanpeng Li <wanpengli@tencent.com>

Introduce some pv check helpers for consistency.

Suggested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 arch/x86/kernel/kvm.c | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index d817f25..76ea8c4 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -425,7 +425,27 @@ static void __init sev_map_percpu_data(void)
 	}
 }
 
+static bool pv_tlb_flush_supported(void)
+{
+	return (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
+		!kvm_para_has_hint(KVM_HINTS_REALTIME) &&
+		kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
+}
+
 #ifdef CONFIG_SMP
+
+static bool pv_ipi_supported(void)
+{
+	return kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI);
+}
+
+static bool pv_sched_yield_supported(void)
+{
+	return (kvm_para_has_feature(KVM_FEATURE_PV_SCHED_YIELD) &&
+		!kvm_para_has_hint(KVM_HINTS_REALTIME) &&
+	    kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
+}
+
 #define KVM_IPI_CLUSTER_SIZE	(2 * BITS_PER_LONG)
 
 static void __send_ipi_mask(const struct cpumask *mask, int vector)
@@ -619,9 +639,7 @@ static void __init kvm_guest_init(void)
 		pv_ops.time.steal_clock = kvm_steal_clock;
 	}
 
-	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)) {
+	if (pv_tlb_flush_supported()) {
 		pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others;
 		pv_ops.mmu.tlb_remove_table = tlb_remove_table;
 	}
@@ -632,9 +650,7 @@ static void __init kvm_guest_init(void)
 #ifdef CONFIG_SMP
 	smp_ops.smp_prepare_cpus = kvm_smp_prepare_cpus;
 	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
-	if (kvm_para_has_feature(KVM_FEATURE_PV_SCHED_YIELD) &&
-	    !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
-	    kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
+	if (pv_sched_yield_supported()) {
 		smp_ops.send_call_func_ipi = kvm_smp_send_call_func_ipi;
 		pr_info("KVM setup pv sched yield\n");
 	}
@@ -700,7 +716,7 @@ static uint32_t __init kvm_detect(void)
 static void __init kvm_apic_init(void)
 {
 #if defined(CONFIG_SMP)
-	if (kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI))
+	if (pv_ipi_supported())
 		kvm_setup_pv_ipi();
 #endif
 }
@@ -739,9 +755,7 @@ static __init int kvm_setup_pv_tlb_flush(void)
 	if (!kvm_para_available() || nopv)
 		return 0;
 
-	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)) {
+	if (pv_tlb_flush_supported()) {
 		for_each_possible_cpu(cpu) {
 			zalloc_cpumask_var_node(per_cpu_ptr(&__pv_tlb_mask, cpu),
 				GFP_KERNEL, cpu_to_node(cpu));
-- 
2.7.4

[PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Wanpeng Li]

From: Wanpeng Li <wanpengli@tencent.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@google.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.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

Re: [PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Wanpeng Li]

ping,
On Tue, 18 Feb 2020 at 09:12, Wanpeng Li <kernellwp@gmail.com> wrote:
>
> From: Wanpeng Li <wanpengli@tencent.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@google.com>
> Acked-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.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
>

Re: [PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Nick Desaulniers]

(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@gmail.com> wrote:
>
> ping,
> On Tue, 18 Feb 2020 at 09:12, Wanpeng Li <kernellwp@gmail.com> wrote:
> >
> > From: Wanpeng Li <wanpengli@tencent.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@google.com>
> > Acked-by: Nick Desaulniers <ndesaulniers@google.com>
> > Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Nick Desaulniers <ndesaulniers@google.com>
> > Signed-off-by: Wanpeng Li <wanpengli@tencent.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

Re: [PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Vitaly Kuznetsov]

Nick Desaulniers <ndesaulniers@google.com> writes:

> (putting Paolo in To: field, in case email filters are to blame.
> Vitaly, maybe you could ping Paolo internally?)
>

I could, but the only difference from what I'm doing right now would
proabbly be the absence of non-@redaht.com emails in To/Cc: fields of
this email :-)

Do we want this fix for one of the last 5.6 RCs or 5.7 would be fine?
Personally, I'd say we're not in a great hurry and 5.7 is OK.

-- 
Vitaly

Re: [PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Paolo Bonzini]

On 26/02/20 14:10, Vitaly Kuznetsov wrote:
> Nick Desaulniers <ndesaulniers@google.com> writes:
> 
>> (putting Paolo in To: field, in case email filters are to blame.
>> Vitaly, maybe you could ping Paolo internally?)
>>
> 
> I could, but the only difference from what I'm doing right now would
> proabbly be the absence of non-@redaht.com emails in To/Cc: fields of
> this email :-)
>
> Do we want this fix for one of the last 5.6 RCs or 5.7 would be fine?
> Personally, I'd say we're not in a great hurry and 5.7 is OK.

I think we can do it for 5.6, but we're not in a great hurry. :)  The
rc4 pull request was already going to be relatively large and I had just
been scolded by Linus so I postponed this, but I am going to include it
this week.

Paolo

Re: [PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Nick Desaulniers]

On Wed, Feb 26, 2020 at 5:27 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 26/02/20 14:10, Vitaly Kuznetsov wrote:
> > Nick Desaulniers <ndesaulniers@google.com> writes:
> >
> >> (putting Paolo in To: field, in case email filters are to blame.
> >> Vitaly, maybe you could ping Paolo internally?)
> >>
> >
> > I could, but the only difference from what I'm doing right now would
> > proabbly be the absence of non-@redaht.com emails in To/Cc: fields of
> > this email :-)
> >
> > Do we want this fix for one of the last 5.6 RCs or 5.7 would be fine?
> > Personally, I'd say we're not in a great hurry and 5.7 is OK.
>
> I think we can do it for 5.6, but we're not in a great hurry. :)  The
> rc4 pull request was already going to be relatively large and I had just
> been scolded by Linus so I postponed this, but I am going to include it
> this week.

No rush; soak time is good.
-- 
Thanks,
~Nick Desaulniers

Re: [PATCH RESEND v2 2/2] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Paolo Bonzini]

On 18/02/20 02:08, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.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@google.com>
> Acked-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.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
>  
> 

Queued now, thanks.

Paolo