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Subject[PATCH AUTOSEL 4.19 013/167] KVM: x86: hyperv: keep track of mismatched VP indexes
Date
From: Vitaly Kuznetsov <vkuznets@redhat.com>

[ Upstream commit 87ee613d076351950b74383215437f841ebbeb75 ]

In most common cases VP index of a vcpu matches its vcpu index. Userspace
is, however, free to set any mapping it wishes and we need to account for
that when we need to find a vCPU with a particular VP index. To keep search
algorithms optimal in both cases introduce 'num_mismatched_vp_indexes'
counter showing how many vCPUs with mismatching VP index we have. In case
the counter is zero we can assume vp_index == vcpu_idx.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/include/asm/kvm_host.h | 3 +++
arch/x86/kvm/hyperv.c | 26 +++++++++++++++++++++++---
2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3245b95ad2d97..b6417454a9d79 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -784,6 +784,9 @@ struct kvm_hv {
u64 hv_reenlightenment_control;
u64 hv_tsc_emulation_control;
u64 hv_tsc_emulation_status;
+
+ /* How many vCPUs have VP index != vCPU index */
+ atomic_t num_mismatched_vp_indexes;
};

enum kvm_irqchip_mode {
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 3f2775aac5545..2bb554b90b3c2 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1045,11 +1045,31 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
struct kvm_vcpu_hv *hv_vcpu = &vcpu->arch.hyperv;

switch (msr) {
- case HV_X64_MSR_VP_INDEX:
- if (!host || (u32)data >= KVM_MAX_VCPUS)
+ case HV_X64_MSR_VP_INDEX: {
+ struct kvm_hv *hv = &vcpu->kvm->arch.hyperv;
+ int vcpu_idx = kvm_vcpu_get_idx(vcpu);
+ u32 new_vp_index = (u32)data;
+
+ if (!host || new_vp_index >= KVM_MAX_VCPUS)
return 1;
- hv_vcpu->vp_index = (u32)data;
+
+ if (new_vp_index == hv_vcpu->vp_index)
+ return 0;
+
+ /*
+ * The VP index is initialized to vcpu_index by
+ * kvm_hv_vcpu_postcreate so they initially match. Now the
+ * VP index is changing, adjust num_mismatched_vp_indexes if
+ * it now matches or no longer matches vcpu_idx.
+ */
+ if (hv_vcpu->vp_index == vcpu_idx)
+ atomic_inc(&hv->num_mismatched_vp_indexes);
+ else if (new_vp_index == vcpu_idx)
+ atomic_dec(&hv->num_mismatched_vp_indexes);
+
+ hv_vcpu->vp_index = new_vp_index;
break;
+ }
case HV_X64_MSR_VP_ASSIST_PAGE: {
u64 gfn;
unsigned long addr;
--
2.20.1
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