linux-kernel - [PATCH] kvm: don't take vcpu mutex for obviously invalid vcpu ioctls

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Message-Id: <1411167805-2458-1-git-send-email-dmatlack@google.com>
Date:	Fri, 19 Sep 2014 16:03:25 -0700
From:	David Matlack <dmatlack@...gle.com>
To:	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	David Matlack <dmatlack@...gle.com>
Subject: [PATCH] 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. If we know ioctl is going to be rejected as invalid anyway,
we can fail before trying to take the vcpu mutex.

This patch does not change functionality, it just makes invalid ioctls
fail faster.

Signed-off-by: David Matlack <dmatlack@...gle.com>
---
 virt/kvm/kvm_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 96ec622..f9234e5 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>
 
@@ -1975,6 +1976,9 @@ 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,
-- 
2.1.0.rc2.206.gedb03e5

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