KVM: VMX: Gracefully handle faults on VMXON

Gracefully handle faults on VMXON, e.g. #GP due to VMX being disabled by
BIOS, instead of letting the fault crash the system.  Now that KVM uses
cpufeatures to query support instead of reading MSR_IA32_FEAT_CTL
directly, it's possible for a bug in a different subsystem to cause KVM
to incorrectly attempt VMXON[*].  Crashing the system is especially
annoying if the system is configured such that hardware_enable() will
be triggered during boot.

Oppurtunistically rename @addr to @vmxon_pointer and use a named param
to reference it in the inline assembly.

Print 0xdeadbeef in the ultra-"rare" case that reading MSR_IA32_FEAT_CTL
also faults.

[*] https://lkml.kernel.org/r/20200226231615.13664-1-sean.j.christopherson@intel.com
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200321193751.24985-4-sean.j.christopherson@intel.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 07634ca..3aba51d 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2218,18 +2218,33 @@ static __init int vmx_disabled_by_bios(void)
               !boot_cpu_has(X86_FEATURE_VMX);
 }
 
-static void kvm_cpu_vmxon(u64 addr)
+static int kvm_cpu_vmxon(u64 vmxon_pointer)
 {
+       u64 msr;
+
        cr4_set_bits(X86_CR4_VMXE);
        intel_pt_handle_vmx(1);
 
-       asm volatile ("vmxon %0" : : "m"(addr));
+       asm_volatile_goto("1: vmxon %[vmxon_pointer]\n\t"
+                         _ASM_EXTABLE(1b, %l[fault])
+                         : : [vmxon_pointer] "m"(vmxon_pointer)
+                         : : fault);
+       return 0;
+
+fault:
+       WARN_ONCE(1, "VMXON faulted, MSR_IA32_FEAT_CTL (0x3a) = 0x%llx\n",
+                 rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr) ? 0xdeadbeef : msr);
+       intel_pt_handle_vmx(0);
+       cr4_clear_bits(X86_CR4_VMXE);
+
+       return -EFAULT;
 }
 
 static int hardware_enable(void)
 {
        int cpu = raw_smp_processor_id();
        u64 phys_addr = __pa(per_cpu(vmxarea, cpu));
+       int r;
 
        if (cr4_read_shadow() & X86_CR4_VMXE)
                return -EBUSY;
@@ -2246,7 +2261,10 @@ static int hardware_enable(void)
        INIT_LIST_HEAD(&per_cpu(blocked_vcpu_on_cpu, cpu));
        spin_lock_init(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
 
-       kvm_cpu_vmxon(phys_addr);
+       r = kvm_cpu_vmxon(phys_addr);
+       if (r)
+               return r;
+
        if (enable_ept)
                ept_sync_global();