[PATCH v2 10/50] KVM: VMX: Reset eVMCS controls in VP assist page during hardware disabling
From: Sean Christopherson <seanjc@google.com>
Date: 2022-11-30 23:11:05
Also in:
kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-mips, linux-riscv, linux-s390, lkml
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
Reset the eVMCS controls in the per-CPU VP assist page during hardware disabling instead of waiting until kvm-intel's module exit. The controls are activated if and only if KVM creates a VM, i.e. don't need to be reset if hardware is never enabled. Doing the reset during hardware disabling will naturally fix a potential NULL pointer deref bug once KVM disables CPU hotplug while enabling and disabling hardware (which is necessary to fix a variety of bugs). If the kernel is running as the root partition, the VP assist page is unmapped during CPU hot unplug, and so KVM's clearing of the eVMCS controls needs to occur with CPU hot(un)plug disabled, otherwise KVM could attempt to write to a CPU's VP assist page after it's unmapped. Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/vmx/vmx.c | 50 +++++++++++++++++++++++++----------------- 1 file changed, 30 insertions(+), 20 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index cea8c07f5229..d85d175dca70 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c@@ -551,6 +551,33 @@ static int hv_enable_l2_tlb_flush(struct kvm_vcpu *vcpu) return 0; } +static void hv_reset_evmcs(void) +{ + struct hv_vp_assist_page *vp_ap; + + if (!static_branch_unlikely(&enable_evmcs)) + return; + + /* + * KVM should enable eVMCS if and only if all CPUs have a VP assist + * page, and should reject CPU onlining if eVMCS is enabled the CPU + * doesn't have a VP assist page allocated. + */ + vp_ap = hv_get_vp_assist_page(smp_processor_id()); + if (WARN_ON_ONCE(!vp_ap)) + return; + + /* + * Reset everything to support using non-enlightened VMCS access later + * (e.g. when we reload the module with enlightened_vmcs=0) + */ + vp_ap->nested_control.features.directhypercall = 0; + vp_ap->current_nested_vmcs = 0; + vp_ap->enlighten_vmentry = 0; +} + +#else /* IS_ENABLED(CONFIG_HYPERV) */ +static void hv_reset_evmcs(void) {} #endif /* IS_ENABLED(CONFIG_HYPERV) */ /*
@@ -2496,6 +2523,8 @@ static void vmx_hardware_disable(void) if (cpu_vmxoff()) kvm_spurious_fault(); + hv_reset_evmcs(); + intel_pt_handle_vmx(0); }
@@ -8462,27 +8491,8 @@ static void vmx_exit(void) kvm_exit(); #if IS_ENABLED(CONFIG_HYPERV) - if (static_branch_unlikely(&enable_evmcs)) { - int cpu; - struct hv_vp_assist_page *vp_ap; - /* - * Reset everything to support using non-enlightened VMCS - * access later (e.g. when we reload the module with - * enlightened_vmcs=0) - */ - for_each_online_cpu(cpu) { - vp_ap = hv_get_vp_assist_page(cpu); - - if (!vp_ap) - continue; - - vp_ap->nested_control.features.directhypercall = 0; - vp_ap->current_nested_vmcs = 0; - vp_ap->enlighten_vmentry = 0; - } - + if (static_branch_unlikely(&enable_evmcs)) static_branch_disable(&enable_evmcs); - } #endif vmx_cleanup_l1d_flush();
--
2.38.1.584.g0f3c55d4c2-goog