Re: [PATCH] KVM: PPC: Book3S HV: Replace kvmppc_find_vcpu() with kvm_get_vcpu()

From: Michael Ellerman <mpe@ellerman.id.au>
To: Thomas Huth <thuth@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>,
	kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, agraf@suse.de,
	gleb@kernel.org, pbonzini@redhat.com, benh@kernel.crashing.org
Subject: Re: [PATCH] KVM: PPC: Book3S HV: Replace kvmppc_find_vcpu() with kvm_get_vcpu()
Date: Fri, 08 May 2015 19:01:07 +1000	[thread overview]
Message-ID: <1431075667.9673.10.camel@ellerman.id.au> (raw)
In-Reply-To: <20150508101904.509c629a@thh440s>

On Fri, 2015-05-08 at 10:19 +0200, Thomas Huth wrote:
> On Fri, 8 May 2015 09:07:18 +1000
> Paul Mackerras <paulus@samba.org> wrote:
> 
> > On Thu, May 07, 2015 at 05:49:39PM +0200, Thomas Huth wrote:
> > > Both functions are doing the same thing - looking up the struct
> > > kvm_vcpu pointer for a given vCPU ID.
> > 
> > No, kvm_get_vcpu(n) returns the n'th vcpu created, which is often
> > but not necessarily the same as the vcpu with id n.  In fact, due to
> > the way we do threading in HV KVM, it's quite common for userspace to
> > create vcpus with ids 0, 8, 16, ..., which means that the n'th vcpu
> > created does not have id n (except of course for vcpu 0).

A patch adding a comment explaining that subtlety would be welcome from anyone
who sent it :)

cheers