[RFC PATCH v2 06/12] KVM: x86: Provide paravirtualized flush_tlb_multi()

Nadav Amit
2019-05-31T06:37:13Z

Support the new interface of flush_tlb_multi, which also flushes the
local CPU's TLB, instead of flush_tlb_others that does not. This
interface is more performant since it parallelize remote and local TLB
flushes.

The actual implementation of flush_tlb_multi() is almost identical to
that of flush_tlb_others().

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Nadav Amit <namit@vmware.com>
---
arch/x86/kernel/kvm.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index c1c2b88ea3f1..86b8267166e6 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -593,7 +593,7 @@ static void __init kvm_apf_trap_init(void)

static DEFINE_PER_CPU(cpumask_var_t, __pv_tlb_mask);

-static void kvm_flush_tlb_others(const struct cpumask *cpumask,
+static void kvm_flush_tlb_multi(const struct cpumask *cpumask,
const struct flush_tlb_info *info)
{
u8 state;
@@ -607,6 +607,11 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask,
* queue flush_on_enter for pre-empted vCPUs
*/
for_each_cpu(cpu, flushmask) {
+ /*
+ * The local vCPU is never preempted, so we do not explicitly
+ * skip check for local vCPU - it will never be cleared from
+ * flushmask.
+ */
src = &per_cpu(steal_time, cpu);
state = READ_ONCE(src->preempted);
if ((state & KVM_VCPU_PREEMPTED)) {
@@ -616,7 +621,7 @@ static void kvm_flush_tlb_others(const struct cpumask *cpumask,
}
}

- native_flush_tlb_others(flushmask, info);
+ native_flush_tlb_multi(flushmask, info);
}

static void __init kvm_guest_init(void)
@@ -641,9 +646,8 @@ static void __init kvm_guest_init(void)
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)) {
- pv_ops.mmu.flush_tlb_others = kvm_flush_tlb_others;
+ pv_ops.mmu.flush_tlb_multi = kvm_flush_tlb_multi;
pv_ops.mmu.tlb_remove_table = tlb_remove_table;
- static_key_disable(&flush_tlb_multi_enabled.key);
}

if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
--
2.20.1