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: [email protected] Signed-off-by: David Matlack <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
cbmeeks · Sep 24, 2014 · 2ea75be · 2ea75be
1 parent 234b239
commit 2ea75be
Showing 1 changed file with 4 additions and 0 deletions.
diff --git 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 @@ static long kvm_vcpu_ioctl(struct file *filp,
 	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,