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

commit 2ea75be3219571d0ec009ce20d9971e54af96e09 upstream.

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.

Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
David Matlack 2014-09-19 16:03:25 -07:00 committed by Greg Kroah-Hartman
parent 68249f03d0
commit 7889ddde27
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>
@ -1981,6 +1982,9 @@ 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,