[PATCH v4 5/8] KVM Guest: Add paravirt kvm_flush_tlb_others

Nikunj A. Dadhania
2012-08-21T11:27:58Z

From: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>

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

v3:
* use only one state variable for vcpu-running/flush_on_enter
* use cmpxchg to update the state
* adapt to Alex Shi's TLB flush optimization

v2:
* use ACCESS_ONCE so the value is not register cached
* Separate HV and Guest code

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

--
Pseudo Algo:
------------
Hypervisor
==========
guest_exit()
if (!(xchg(state, NOT_IN_GUEST) == SHOULD_FLUSH))
tlb_flush(vcpu);

guest_enter()
if (!(xchg(state, IN_GUEST) == SHOULD_FLUSH))
tlb_flush(vcpu);

Guest
=====
flushcpumask = cpumask;
for_each_cpu(i, flushmask) {
state = vs->state;
if(!test_bit(IN_GUEST_MODE, state)) {
if (cmpxchg(&vs->state, state,
state | (1 << SHOULD_FLUSH)) == SUCCESS)
cpumask_clear_cpu(flushmask,i)
}
}

smp_call_function_many(f->flushmask, flush_tlb_func)
---
arch/x86/include/asm/tlbflush.h | 11 +++++++++++
arch/x86/kernel/kvm.c | 4 +++-
arch/x86/mm/tlb.c | 36 ++++++++++++++++++++++++++++++++++++
3 files changed, 50 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 74a4433..0a343a1 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -119,6 +119,13 @@ 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 start,
+ unsigned long end)
+{
+}
+
static inline void reset_lazy_tlbstate(void)
{
}
@@ -153,6 +160,10 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
struct mm_struct *mm,
unsigned long start, unsigned long end);

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

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 37e6599..b538a31 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -501,8 +501,10 @@ void __init kvm_guest_init(void)
apic_set_eoi_write(kvm_guest_apic_eoi_write);

#ifdef CONFIG_PARAVIRT_TLB_FLUSH
- if (kvm_para_has_feature(KVM_FEATURE_VCPU_STATE))
+ if (kvm_para_has_feature(KVM_FEATURE_VCPU_STATE)) {
has_vcpu_state = 1;
+ pv_mmu_ops.flush_tlb_others = kvm_flush_tlb_others;
+ }
#endif

#ifdef CONFIG_SMP
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 613cd83..645df99 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>
@@ -119,6 +120,41 @@ static void flush_tlb_func(void *info)

}

+#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 start,
+ unsigned long end)
+{
+ struct flush_tlb_info info;
+ struct kvm_vcpu_state *v_state;
+ u64 state;
+ int cpu;
+ cpumask_t flushmask;
+
+ cpumask_copy(&flushmask, cpumask);
+ info.flush_mm = mm;
+ info.flush_start = start;
+ info.flush_end = end;
+ /*
+ * We have to call flush only on online vCPUs. And
+ * queue flush_on_enter for pre-empted vCPUs
+ */
+ for_each_cpu(cpu, to_cpumask(&flushmask)) {
+ v_state = &per_cpu(vcpu_state, cpu);
+ state = v_state->state;
+ if (!test_bit(KVM_VCPU_STATE_IN_GUEST_MODE, &state)) {
+ if (cmpxchg(&v_state->state, state, state | 1 << KVM_VCPU_STATE_SHOULD_FLUSH))
+ cpumask_clear_cpu(cpu, to_cpumask(&flushmask));
+ }
+ }
+
+ smp_call_function_many(&flushmask, flush_tlb_func, &info, 1);
+}
+#endif /* CONFIG_KVM_GUEST */
+
void native_flush_tlb_others(const struct cpumask *cpumask,
struct mm_struct *mm, unsigned long start,
unsigned long end)