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Subject[PATCH v2 3/7] KVM: Add paravirt kvm_flush_tlb_others
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flush_tlb_others_ipi depends on lot of statics in tlb.c.  Replicated
the flush_tlb_others_ipi as kvm_flush_tlb_others to further adapt to
paravirtualization.

Use the vcpu state information inside the kvm_flush_tlb_others to
avoid sending ipi to pre-empted vcpus.

* Do not send ipi's to offline vcpus and set flush_on_enter flag
* For online vcpus: Wait for them to clear the flag

The approach was discussed here: https://lkml.org/lkml/2012/2/20/157

Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>

--
Pseudo Algo:

Write()
======

guest_exit()
flush_on_enter[i]=0;
running[i] = 0;

guest_enter()
running[i] = 1;
smp_mb();
if(flush_on_enter[i]) {
tlb_flush()
flush_on_enter[i]=0;
}


Read()
======

GUEST KVM-HV

f->flushcpumask = cpumask - me;

again:
for_each_cpu(i, f->flushmask) {

if (!running[i]) {
case 1:

running[n]=1

(cpuN does not see
flush_on_enter set,
guest later finds it
running and sends ipi,
we are fine here, need
to clear the flag on
guest_exit)

flush_on_enter[i] = 1;
case2:

running[n]=1
(cpuN - will see flush
on enter and an IPI as
well - addressed in patch-4)

if (!running[i])
cpu_clear(f->flushmask); All is well, vm_enter
will do the fixup
}
case 3:
running[n] = 0;

(cpuN went to sleep,
we saw it as awake,
ipi sent, but wait
will break without
zero_mask and goto
again will take care)

}
send_ipi(f->flushmask)

wait_a_while_for_zero_mask();

if (!zero_mask)
goto again;
---
arch/x86/include/asm/kvm_para.h | 3 +-
arch/x86/include/asm/tlbflush.h | 9 ++++++
arch/x86/kernel/kvm.c | 1 +
arch/x86/kvm/x86.c | 14 ++++++++-
arch/x86/mm/tlb.c | 61 +++++++++++++++++++++++++++++++++++++++
5 files changed, 86 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index f57b5cc..684a285 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -55,7 +55,8 @@ struct kvm_steal_time {

struct kvm_vcpu_state {
__u32 state;
- __u32 pad[15];
+ __u32 flush_on_enter;
+ __u32 pad[14];
};

#define KVM_VCPU_STATE_ALIGN_BITS 5
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index c0e108e..29470bd 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -119,6 +119,12 @@ static inline void native_flush_tlb_others(const struct cpumask *cpumask,
{
}

+static inline void kvm_flush_tlb_others(const struct cpumask *cpumask,
+ struct mm_struct *mm,
+ unsigned long va)
+{
+}
+
static inline void reset_lazy_tlbstate(void)
{
}
@@ -145,6 +151,9 @@ static inline void flush_tlb_range(struct vm_area_struct *vma,
void native_flush_tlb_others(const struct cpumask *cpumask,
struct mm_struct *mm, unsigned long va);

+void kvm_flush_tlb_others(const struct cpumask *cpumask,
+ struct mm_struct *mm, unsigned long va);
+
#define TLBSTATE_OK 1
#define TLBSTATE_LAZY 2

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index bb686a6..66db54e 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -465,6 +465,7 @@ void __init kvm_guest_init(void)
}

has_vcpu_state = 1;
+ pv_mmu_ops.flush_tlb_others = kvm_flush_tlb_others;

#ifdef CONFIG_SMP
smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 264f172..4714a7b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1548,9 +1548,20 @@ static void kvm_set_vcpu_state(struct kvm_vcpu *vcpu)
if (!(vcpu->arch.v_state.msr_val & KVM_MSR_ENABLED))
return;

+ /*
+ * Let the guest know that we are online, make sure we do not
+ * overwrite flush_on_enter, just write the vs->state.
+ */
vs->state = 1;
- kvm_write_guest_cached(vcpu->kvm, ghc, vs, 2*sizeof(__u32));
+ kvm_write_guest_cached(vcpu->kvm, ghc, vs, 1*sizeof(__u32));
smp_wmb();
+ /*
+ * Guest might have seen us offline and would have set
+ * flush_on_enter.
+ */
+ kvm_read_guest_cached(vcpu->kvm, ghc, vs, 2*sizeof(__u32));
+ if (vs->flush_on_enter)
+ kvm_x86_ops->tlb_flush(vcpu);
}

static void kvm_clear_vcpu_state(struct kvm_vcpu *vcpu)
@@ -1561,6 +1572,7 @@ static void kvm_clear_vcpu_state(struct kvm_vcpu *vcpu)
if (!(vcpu->arch.v_state.msr_val & KVM_MSR_ENABLED))
return;

+ vs->flush_on_enter = 0;
vs->state = 0;
kvm_write_guest_cached(vcpu->kvm, ghc, vs, 2*sizeof(__u32));
smp_wmb();
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index d6c0418..f5dacdd 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -6,6 +6,7 @@
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/cpu.h>
+#include <linux/kvm_para.h>

#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
@@ -202,6 +203,66 @@ static void flush_tlb_others_ipi(const struct cpumask *cpumask,
raw_spin_unlock(&f->tlbstate_lock);
}

+#ifdef CONFIG_KVM_GUEST
+
+DECLARE_PER_CPU(struct kvm_vcpu_state, vcpu_state) __aligned(64);
+
+void kvm_flush_tlb_others(const struct cpumask *cpumask,
+ struct mm_struct *mm, unsigned long va)
+{
+ unsigned int sender;
+ union smp_flush_state *f;
+ int cpu, loop;
+ struct kvm_vcpu_state *v_state;
+
+ /* Caller has disabled preemption */
+ sender = this_cpu_read(tlb_vector_offset);
+ f = &flush_state[sender];
+
+ if (nr_cpu_ids > NUM_INVALIDATE_TLB_VECTORS)
+ raw_spin_lock(&f->tlbstate_lock);
+
+ f->flush_mm = mm;
+ f->flush_va = va;
+ if (cpumask_andnot(to_cpumask(f->flush_cpumask), cpumask, cpumask_of(smp_processor_id()))) {
+ /*
+ * We have to send the IPI only to online vCPUs
+ * affected. And queue flush_on_enter for pre-empted
+ * vCPUs
+ */
+again:
+ for_each_cpu(cpu, to_cpumask(f->flush_cpumask)) {
+ v_state = &per_cpu(vcpu_state, cpu);
+
+ if (!v_state->state) {
+ v_state->flush_on_enter = 1;
+ smp_mb();
+ if (!v_state->state)
+ cpumask_clear_cpu(cpu, to_cpumask(f->flush_cpumask));
+ }
+ }
+
+ if (cpumask_empty(to_cpumask(f->flush_cpumask)))
+ goto out;
+
+ apic->send_IPI_mask(to_cpumask(f->flush_cpumask),
+ INVALIDATE_TLB_VECTOR_START + sender);
+
+ loop = 1000;
+ while (!cpumask_empty(to_cpumask(f->flush_cpumask)) && --loop)
+ cpu_relax();
+
+ if (!cpumask_empty(to_cpumask(f->flush_cpumask)))
+ goto again;
+ }
+out:
+ f->flush_mm = NULL;
+ f->flush_va = 0;
+ if (nr_cpu_ids > NUM_INVALIDATE_TLB_VECTORS)
+ raw_spin_unlock(&f->tlbstate_lock);
+}
+#endif /* CONFIG_KVM_GUEST */
+
void native_flush_tlb_others(const struct cpumask *cpumask,
struct mm_struct *mm, unsigned long va)
{


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