KVM: x86: drop calling kvm_mmu_zap_all in emulator_fix_hypercall

Quote Gleb's mail:

| Back then kvm->lock protected memslot access so code like:
|
| mutex_lock(&vcpu->kvm->lock);
| kvm_mmu_zap_all(vcpu->kvm);
| mutex_unlock(&vcpu->kvm->lock);
|
| which is what 7aa81cc does was enough to guaranty that no vcpu will
| run while code is patched. This is no longer the case and
| mutex_lock(&vcpu->kvm->lock); is gone from that code path long time ago,
| so now kvm_mmu_zap_all() there is useless and the code is incorrect.

So we drop it and it will be fixed later

Signed-off-by: Xiao Guangrong <[email protected]>
Reviewed-by: Marcelo Tosatti <[email protected]>
Signed-off-by: Gleb Natapov <[email protected]>

Author: Xiao Guangrong

arch/x86/kvm/x86.c

@@ -5523,13 +5523,6 @@ static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt)
 	char instruction[3];
 	unsigned long rip = kvm_rip_read(vcpu);
 
-	/*
-	 * Blow out the MMU to ensure that no other VCPU has an active mapping
-	 * to ensure that the updated hypercall appears atomically across all
-	 * VCPUs.
-	 */
-	kvm_mmu_zap_all(vcpu->kvm);
-
 	kvm_x86_ops->patch_hypercall(vcpu, instruction);
 
 	return emulator_write_emulated(ctxt, rip, instruction, 3, NULL);