[RFC PATCH v6 05/36] KVM: x86: Report error when setting CPUID if Hyper-V allocation fails

Sean Christopherson
2022-08-24T03:03:43Z

Return -ENOMEM back to userspace if allocating the Hyper-V vCPU struct
fails when enabling Hyper-V in guest CPUID. Silently ignoring failure
means that KVM will not have an up-to-date CPUID cache if allocating the
struct succeeds later on, e.g. when activating SynIC.

Rejecting the CPUID operation also guarantess that vcpu->arch.hyperv is
non-NULL if hyperv_enabled is true, which will allow for additional
cleanup, e.g. in the eVMCS code.

Note, the initialization needs to be done before CPUID is set, and more
subtly before kvm_check_cpuid(), which potentially enables dynamic
XFEATURES. Sadly, there's no easy way to avoid exposing Hyper-V details
to CPUID or vice versa. Expose kvm_hv_vcpu_init() and the Hyper-V CPUID
signature to CPUID instead of exposing cpuid_entry2_find() outside of
CPUID code. It's hard to envision kvm_hv_vcpu_init() being misused,
whereas cpuid_entry2_find() absolutely shouldn't be used outside of core
CPUID code.

Fixes: 10d7bf1e46dc ("KVM: x86: hyper-v: Cache guest CPUID leaves determining features availability")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/cpuid.c | 18 +++++++++++++++++-
arch/x86/kvm/hyperv.c | 30 ++++++++++++++----------------
arch/x86/kvm/hyperv.h | 6 +++++-
3 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 75dcf7a72605..ffdc28684cb7 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -311,6 +311,15 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
}
EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);

+static bool kvm_cpuid_has_hyperv(struct kvm_cpuid_entry2 *entries, int nent)
+{
+ struct kvm_cpuid_entry2 *entry;
+
+ entry = cpuid_entry2_find(entries, nent, HYPERV_CPUID_INTERFACE,
+ KVM_CPUID_INDEX_NOT_SIGNIFICANT);
+ return entry && entry->eax == HYPERV_CPUID_SIGNATURE_EAX;
+}
+
static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
{
struct kvm_lapic *apic = vcpu->arch.apic;
@@ -341,7 +350,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
vcpu->arch.cr4_guest_rsvd_bits =
__cr4_reserved_bits(guest_cpuid_has, vcpu);

- kvm_hv_set_cpuid(vcpu);
+ kvm_hv_set_cpuid(vcpu, kvm_cpuid_has_hyperv(vcpu->arch.cpuid_entries,
+ vcpu->arch.cpuid_nent));

/* Invoke the vendor callback only after the above state is updated. */
static_call(kvm_x86_vcpu_after_set_cpuid)(vcpu);
@@ -404,6 +414,12 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
return 0;
}

+ if (kvm_cpuid_has_hyperv(e2, nent)) {
+ r = kvm_hv_vcpu_init(vcpu);
+ if (r)
+ return r;
+ }
+
r = kvm_check_cpuid(vcpu, e2, nent);
if (r)
return r;
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 8aadd31ed058..bf4729e8cc80 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -38,9 +38,6 @@
#include "irq.h"
#include "fpu.h"

-/* "Hv#1" signature */
-#define HYPERV_CPUID_SIGNATURE_EAX 0x31237648
-
#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 64)

static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer,
@@ -934,7 +931,7 @@ static void stimer_init(struct kvm_vcpu_hv_stimer *stimer, int timer_index)
stimer_prepare_msg(stimer);
}

-static int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
+int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
{
struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
int i;
@@ -1984,26 +1981,27 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
return HV_STATUS_SUCCESS;
}

-void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu)
+void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu, bool hyperv_enabled)
{
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
struct kvm_cpuid_entry2 *entry;
- struct kvm_vcpu_hv *hv_vcpu;

- entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_INTERFACE);
- if (entry && entry->eax == HYPERV_CPUID_SIGNATURE_EAX) {
- vcpu->arch.hyperv_enabled = true;
- } else {
- vcpu->arch.hyperv_enabled = false;
+ vcpu->arch.hyperv_enabled = hyperv_enabled;
+
+ if (!hv_vcpu) {
+ /*
+ * KVM should have already allocated kvm_vcpu_hv if Hyper-V is
+ * enabled in CPUID.
+ */
+ WARN_ON_ONCE(vcpu->arch.hyperv_enabled);
return;
}

- if (kvm_hv_vcpu_init(vcpu))
- return;
-
- hv_vcpu = to_hv_vcpu(vcpu);
-
memset(&hv_vcpu->cpuid_cache, 0, sizeof(hv_vcpu->cpuid_cache));

+ if (!vcpu->arch.hyperv_enabled)
+ return;
+
entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_FEATURES);
if (entry) {
hv_vcpu->cpuid_cache.features_eax = entry->eax;
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index da2737f2a956..1030b1b50552 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -23,6 +23,9 @@

#include <linux/kvm_host.h>

+/* "Hv#1" signature */
+#define HYPERV_CPUID_SIGNATURE_EAX 0x31237648
+
/*
* The #defines related to the synthetic debugger are required by KDNet, but
* they are not documented in the Hyper-V TLFS because the synthetic debugger
@@ -141,7 +144,8 @@ void kvm_hv_request_tsc_page_update(struct kvm *kvm);

void kvm_hv_init_vm(struct kvm *kvm);
void kvm_hv_destroy_vm(struct kvm *kvm);
-void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu);
+int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu);
+void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu, bool hyperv_enabled);
int kvm_hv_set_enforce_cpuid(struct kvm_vcpu *vcpu, bool enforce);
int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args);
int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
--
2.37.1.595.g718a3a8f04-goog