From: Marcelo Tosatti <mtosatti@redhat.com>
To: David Matlack <dmatlack@google.com>
Cc: Gleb Natapov <gleb@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kvm: don't take vcpu mutex for obviously invalid vcpu ioctls
Date: Mon, 22 Sep 2014 17:08:12 -0300 [thread overview]
Message-ID: <20140922200812.GA9217@amt.cnet> (raw)
In-Reply-To: <1411167805-2458-1-git-send-email-dmatlack@google.com>
On Fri, Sep 19, 2014 at 04:03:25PM -0700, David Matlack wrote:
> vcpu ioctls can hang the calling thread if issued while a vcpu is
> running.
There is a mutex per-vcpu, so thats expected, OK...
> If we know ioctl is going to be rejected as invalid anyway,
> we can fail before trying to take the vcpu mutex.
Consider a valid ioctl that takes the vcpu mutex. If you need immediate
access for that valid ioctl, it is necessary to interrupt thread
which KVM_RUN ioctl executes.
So knowledge of whether KVM_RUN is being executed is expected in
userspace (either
that or ask the KVM_RUN thread to run the ioctl for you, as qemu does).
Can't see why having different behaviour for valid/invalid ioctls
is a good thing.
> This patch does not change functionality, it just makes invalid ioctls
> fail faster.
Should not be executing vcpu ioctls without interrupt KVM_RUN in the
first place.
next prev parent reply other threads:[~2014-09-22 20:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-19 23:03 [PATCH] kvm: don't take vcpu mutex for obviously invalid vcpu ioctls David Matlack
2014-09-22 10:50 ` Paolo Bonzini
2014-09-22 13:45 ` Christian Borntraeger
2014-09-22 14:31 ` Paolo Bonzini
2014-09-22 18:35 ` David Matlack
2014-09-22 19:20 ` Christian Borntraeger
2014-09-22 19:29 ` Paolo Bonzini
2014-09-23 6:49 ` Gleb Natapov
2014-09-23 8:06 ` Christian Borntraeger
2014-09-23 8:23 ` Paolo Bonzini
2014-09-22 19:40 ` David Matlack
2014-09-22 20:08 ` Marcelo Tosatti [this message]
2014-09-22 21:29 ` Paolo Bonzini
2014-09-22 23:00 ` Marcelo Tosatti
2014-09-22 22:58 ` David Matlack
2014-09-23 0:13 ` Marcelo Tosatti
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