kvm: x86: hyperv: make VP_INDEX managed by userspace

Hyper-V identifies vCPUs by Virtual Processor Index, which can be
queried via HV_X64_MSR_VP_INDEX msr.  It is defined by the spec as a
sequential number which can't exceed the maximum number of vCPUs per VM.
APIC ids can be sparse and thus aren't a valid replacement for VP
indices.

Current KVM uses its internal vcpu index as VP_INDEX.  However, to make
it predictable and persistent across VM migrations, the userspace has to
control the value of VP_INDEX.

This patch achieves that, by storing vp_index explicitly on vcpu, and
allowing HV_X64_MSR_VP_INDEX to be set from the host side.  For
compatibility it's initialized to KVM vcpu index.  Also a few variables
are renamed to make clear distinction betweed this Hyper-V vp_index and
KVM vcpu_id (== APIC id).  Besides, a new capability,
KVM_CAP_HYPERV_VP_INDEX, is added to allow the userspace to skip
attempting msr writes where unsupported, to avoid spamming error logs.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 78ac577c93781b779c7f99112852a7df45bad0b5..e63a35fafef0e153c30023e92622111006d1dd7c 100644 (file)
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -4338,3 +4338,12 @@ This capability enables a newer version of Hyper-V Synthetic interrupt
 controller (SynIC).  The only difference with KVM_CAP_HYPERV_SYNIC is that KVM
 doesn't clear SynIC message and event flags pages when they are enabled by
 writing to the respective MSRs.
+
+8.12 KVM_CAP_HYPERV_VP_INDEX
+
+Architectures: x86
+
+This capability indicates that userspace can load HV_X64_MSR_VP_INDEX msr.  Its
+value is used to denote the target vcpu for a SynIC interrupt.  For
+compatibilty, KVM initializes this msr to KVM's internal vcpu index.  When this
+capability is absent, userspace can still query this msr's value.

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index da3261e384d3a19d15560b26d0b11a7064e1cc19..87ac4fba6d8e12f07e8a9f191bdb028a1c3e6234 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -467,6 +467,7 @@ struct kvm_vcpu_hv_synic {
 
 /* Hyper-V per vcpu emulation context */
 struct kvm_vcpu_hv {
+       u32 vp_index;
        u64 hv_vapic;
        s64 runtime_offset;
        struct kvm_vcpu_hv_synic synic;

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index a8084406707e3a068b74a0779f1176f55785e553..2695a34fa1c5190f98b9fdd092e9cc2d3e44b2a0 100644 (file)
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -106,14 +106,27 @@ static int synic_set_sint(struct kvm_vcpu_hv_synic *synic, int sint,
        return 0;
 }
 
-static struct kvm_vcpu_hv_synic *synic_get(struct kvm *kvm, u32 vcpu_id)
+static struct kvm_vcpu *get_vcpu_by_vpidx(struct kvm *kvm, u32 vpidx)
+{
+       struct kvm_vcpu *vcpu = NULL;
+       int i;
+
+       if (vpidx < KVM_MAX_VCPUS)
+               vcpu = kvm_get_vcpu(kvm, vpidx);
+       if (vcpu && vcpu_to_hv_vcpu(vcpu)->vp_index == vpidx)
+               return vcpu;
+       kvm_for_each_vcpu(i, vcpu, kvm)
+               if (vcpu_to_hv_vcpu(vcpu)->vp_index == vpidx)
+                       return vcpu;
+       return NULL;
+}
+
+static struct kvm_vcpu_hv_synic *synic_get(struct kvm *kvm, u32 vpidx)
 {
        struct kvm_vcpu *vcpu;
        struct kvm_vcpu_hv_synic *synic;
 
-       if (vcpu_id >= atomic_read(&kvm->online_vcpus))
-               return NULL;
-       vcpu = kvm_get_vcpu(kvm, vcpu_id);
+       vcpu = get_vcpu_by_vpidx(kvm, vpidx);
        if (!vcpu)
                return NULL;
        synic = vcpu_to_synic(vcpu);
@@ -320,11 +333,11 @@ static int synic_set_irq(struct kvm_vcpu_hv_synic *synic, u32 sint)
        return ret;
 }
 
-int kvm_hv_synic_set_irq(struct kvm *kvm, u32 vcpu_id, u32 sint)
+int kvm_hv_synic_set_irq(struct kvm *kvm, u32 vpidx, u32 sint)
 {
        struct kvm_vcpu_hv_synic *synic;
 
-       synic = synic_get(kvm, vcpu_id);
+       synic = synic_get(kvm, vpidx);
        if (!synic)
                return -EINVAL;
 
@@ -343,11 +356,11 @@ void kvm_hv_synic_send_eoi(struct kvm_vcpu *vcpu, int vector)
                        kvm_hv_notify_acked_sint(vcpu, i);
 }
 
-static int kvm_hv_set_sint_gsi(struct kvm *kvm, u32 vcpu_id, u32 sint, int gsi)
+static int kvm_hv_set_sint_gsi(struct kvm *kvm, u32 vpidx, u32 sint, int gsi)
 {
        struct kvm_vcpu_hv_synic *synic;
 
-       synic = synic_get(kvm, vcpu_id);
+       synic = synic_get(kvm, vpidx);
        if (!synic)
                return -EINVAL;
 
@@ -689,6 +702,13 @@ void kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
                stimer_init(&hv_vcpu->stimer[i], i);
 }
 
+void kvm_hv_vcpu_postcreate(struct kvm_vcpu *vcpu)
+{
+       struct kvm_vcpu_hv *hv_vcpu = vcpu_to_hv_vcpu(vcpu);
+
+       hv_vcpu->vp_index = kvm_vcpu_get_idx(vcpu);
+}
+
 int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages)
 {
        struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu);
@@ -983,6 +1003,11 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
        struct kvm_vcpu_hv *hv = &vcpu->arch.hyperv;
 
        switch (msr) {
+       case HV_X64_MSR_VP_INDEX:
+               if (!host)
+                       return 1;
+               hv->vp_index = (u32)data;
+               break;
        case HV_X64_MSR_APIC_ASSIST_PAGE: {
                u64 gfn;
                unsigned long addr;
@@ -1094,18 +1119,9 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
        struct kvm_vcpu_hv *hv = &vcpu->arch.hyperv;
 
        switch (msr) {
-       case HV_X64_MSR_VP_INDEX: {
-               int r;
-               struct kvm_vcpu *v;
-
-               kvm_for_each_vcpu(r, v, vcpu->kvm) {
-                       if (v == vcpu) {
-                               data = r;
-                               break;
-                       }
-               }
+       case HV_X64_MSR_VP_INDEX:
+               data = hv->vp_index;
                break;
-       }
        case HV_X64_MSR_EOI:
                return kvm_hv_vapic_msr_read(vcpu, APIC_EOI, pdata);
        case HV_X64_MSR_ICR:

diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index 12f65fe1011d5ae4369ca8e1fa228b5680f889d9..e637631a9574feb5c5c5e0053a46d1b3f29d8646 100644 (file)
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -59,6 +59,7 @@ void kvm_hv_synic_send_eoi(struct kvm_vcpu *vcpu, int vector);
 int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages);
 
 void kvm_hv_vcpu_init(struct kvm_vcpu *vcpu);
+void kvm_hv_vcpu_postcreate(struct kvm_vcpu *vcpu);
 void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu);
 
 static inline struct kvm_vcpu_hv_stimer *vcpu_to_stimer(struct kvm_vcpu *vcpu,

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6753f09827914a83946e20f012ca7e17cce446e7..5b8f07889f6a591f4e23ac69c6bb9656e7bc0a31 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2666,6 +2666,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
        case KVM_CAP_HYPERV_SPIN:
        case KVM_CAP_HYPERV_SYNIC:
        case KVM_CAP_HYPERV_SYNIC2:
+       case KVM_CAP_HYPERV_VP_INDEX:
        case KVM_CAP_PCI_SEGMENT:
        case KVM_CAP_DEBUGREGS:
        case KVM_CAP_X86_ROBUST_SINGLESTEP:
@@ -7688,6 +7689,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
        struct msr_data msr;
        struct kvm *kvm = vcpu->kvm;
 
+       kvm_hv_vcpu_postcreate(vcpu);
+
        if (vcpu_load(vcpu))
                return;
        msr.data = 0x0;

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 38b2cfbc81120a9cfdc2d4a0df3e128cd5ff82fe..6cd63c18708ae1d23dbc280ed49aed55f817a2f5 100644 (file)
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -928,6 +928,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_PPC_FWNMI 146
 #define KVM_CAP_PPC_SMT_POSSIBLE 147
 #define KVM_CAP_HYPERV_SYNIC2 148
+#define KVM_CAP_HYPERV_VP_INDEX 149
 
 #ifdef KVM_CAP_IRQ_ROUTING