kvm: don't take vcpu mutex for obviously invalid vcpu ioctls
vcpu ioctls can hang the calling thread if issued while a vcpu is running.
However, invalid ioctls can happen when userspace tries to probe the kind
of file descriptors (e.g. isatty() calls ioctl(TCGETS)); in that case,
we know the ioctl is going to be rejected as invalid anyway and we can
fail before trying to take the vcpu mutex.
This patch does not change functionality, it just makes invalid ioctls
fail faster.
Cc: stable@vger.kernel.org
Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1c6e847..ff42b11 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -52,6 +52,7 @@
#include <asm/processor.h>
#include <asm/io.h>
+#include <asm/ioctl.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -2032,6 +2033,9 @@
if (vcpu->kvm->mm != current->mm)
return -EIO;
+ if (unlikely(_IOC_TYPE(ioctl) != KVMIO))
+ return -EINVAL;
+
#if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
/*
* Special cases: vcpu ioctls that are asynchronous to vcpu execution,