KVM: SVM: Don't BUG if userspace injects an interrupt with GIF=0

Don't BUG/WARN on interrupt injection due to GIF being cleared,
since it's trivial for userspace to force the situation via
KVM_SET_VCPU_EVENTS (even if having at least a WARN there would be correct
for KVM internally generated injections).

  kernel BUG at arch/x86/kvm/svm/svm.c:3386!
  invalid opcode: 0000 [#1] SMP
  CPU: 15 PID: 926 Comm: smm_test Not tainted 5.17.0-rc3+ #264
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:svm_inject_irq+0xab/0xb0 [kvm_amd]
  Code: <0f> 0b 0f 1f 00 0f 1f 44 00 00 80 3d ac b3 01 00 00 55 48 89 f5 53
  RSP: 0018:ffffc90000b37d88 EFLAGS: 00010246
  RAX: 0000000000000000 RBX: ffff88810a234ac0 RCX: 0000000000000006
  RDX: 0000000000000000 RSI: ffffc90000b37df7 RDI: ffff88810a234ac0
  RBP: ffffc90000b37df7 R08: ffff88810a1fa410 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
  R13: ffff888109571000 R14: ffff88810a234ac0 R15: 0000000000000000
  FS:  0000000001821380(0000) GS:ffff88846fdc0000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f74fc550008 CR3: 000000010a6fe000 CR4: 0000000000350ea0
  Call Trace:
   <TASK>
   inject_pending_event+0x2f7/0x4c0 [kvm]
   kvm_arch_vcpu_ioctl_run+0x791/0x17a0 [kvm]
   kvm_vcpu_ioctl+0x26d/0x650 [kvm]
   __x64_sys_ioctl+0x82/0xb0
   do_syscall_64+0x3b/0xc0
   entry_SYSCALL_64_after_hwframe+0x44/0xae
   </TASK>

Fixes: 219b65dc ("KVM: SVM: Improve nested interrupt injection")
Cc: stable@vger.kernel.org
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <35426af6e123cbe91ec7ce5132ce72521f02b1b5.1651440202.git.maciej.szmigiero@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -3392,8 +3392,6 @@ static void svm_inject_irq(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	BUG_ON(!(gif_set(svm)));
-
 	trace_kvm_inj_virq(vcpu->arch.interrupt.nr);
 	++vcpu->stat.irq_injections;