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

commit 2ea75be321 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>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>
This commit is contained in:
David Matlack 2014-09-19 16:03:25 -07:00 committed by Zefan Li
parent 92f961b3bf
commit 21ff5d9355
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>
@ -1744,6 +1745,9 @@ 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)
/*
* Special cases: vcpu ioctls that are asynchronous to vcpu execution,