[PATCH 27/30] KVM: x86: add force_intercept_exceptions_mask

[Maxim Levitsky]

This parameter will be used by VMX and SVM code to force
interception of a set of exceptions, given by a bitmask
for guest debug and/or kvm debug.

This is based on an idea first shown here:
https://patchwork.kernel.org/project/kvm/patch/20160301192822.GD22677@pd.tnic/

CC: Borislav Petkov <bp at suse.de>
Signed-off-by: Maxim Levitsky <mlevitsk at redhat.com>
---
 arch/x86/include/asm/kvm_host.h | 7 +++++++
 arch/x86/kvm/x86.c              | 9 +++++++++
 arch/x86/kvm/x86.h              | 5 +++++
 3 files changed, 21 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 428ab1cc7dd34..fa498612839a0 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1168,6 +1168,13 @@ struct kvm_arch {
 	struct kvm_pmu_event_filter __rcu *pmu_event_filter;
 	struct task_struct *nx_lpage_recovery_thread;
 
+	/*
+	 * Bitmask of exceptions that KVM will intercept
+	 * and forward to the guest, even if that is not needed
+	 * for normal operation. Debug feature.
+	 */
+	u32 force_intercept_exceptions_bitmask;
+
 #ifdef CONFIG_X86_64
 	/*
 	 * Whether the TDP MMU is enabled for this VM. This contains a
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 63d84c373e465..202c34697852f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -193,6 +193,13 @@ module_param(enable_pmu, bool, 0444);
 bool __read_mostly eager_page_split = true;
 module_param(eager_page_split, bool, 0644);
 
+/*
+ * force_intercept_exceptions_mask is a writable param and its value
+ * is snapshotted when a VM is created
+ */
+static uint force_intercept_exceptions_mask;
+module_param(force_intercept_exceptions_mask, uint, S_IRUGO | S_IWUSR);
+
 /*
  * Restoring the host value for MSRs that are only consumed when running in
  * usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU
@@ -11646,6 +11653,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
 
 	kvm->arch.guest_can_read_msr_platform_info = true;
+	kvm->arch.force_intercept_exceptions_bitmask = force_intercept_exceptions_mask;
 
 #if IS_ENABLED(CONFIG_HYPERV)
 	spin_lock_init(&kvm->arch.hv_root_tdp_lock);
@@ -12886,6 +12894,7 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
 }
 EXPORT_SYMBOL_GPL(kvm_sev_es_string_io);
 
+
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index e9b303b21f173..34f96f483c7e5 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -91,6 +91,11 @@ static inline bool kvm_exception_is_soft(unsigned int nr)
 	return (nr == BP_VECTOR) || (nr == OF_VECTOR);
 }
 
+static inline bool kvm_is_exception_force_intercepted(struct kvm *kvm, int exception)
+{
+	return kvm->arch.force_intercept_exceptions_bitmask & BIT(exception);
+}
+
 static inline bool is_protmode(struct kvm_vcpu *vcpu)
 {
 	return kvm_read_cr0_bits(vcpu, X86_CR0_PE);
-- 
2.26.3