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kvm: don't take vcpu mutex for obviously invalid vcpu ioctls

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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>
This commit is contained in:
David Matlack 2014-09-19 16:03:25 -07:00 committed by Paolo Bonzini
parent 234b239bea
commit 2ea75be321
1 changed files with 4 additions and 0 deletions
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4
virt/kvm/kvm_main.c
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@ -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,