From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [PATCH 3/3] KVM: PPC: Book3S: Add support for hwrng found on some powernv systems Date: Thu, 03 Oct 2013 08:02:20 +1000 Message-ID: <1380751340.645.68.camel@pasglop> References: <5243F933.7000907@redhat.com> <20131001083426.GB27484@concordia> <20131001083908.GA17294@redhat.com> <1380620338.645.22.camel@pasglop> <524AAFAA.3010801@redhat.com> <20131002050940.GA25363@drongo> <524BDD73.3020106@redhat.com> <1380704789.645.57.camel@pasglop> <668E4650-BC22-4CBF-A282-E7875DF29DB6@suse.de> <3CBF5732-E7EE-4C96-8132-6D7B77270DAF@suse.de> <20131002100224.GF17294@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: tytso@mit.edu, kvm@vger.kernel.org, linuxppc-dev@ozlabs.org, Alexander Graf , kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, herbert@gondor.hengli.com.au, Paul Mackerras , mpm@selenic.com, Paolo Bonzini To: Gleb Natapov Return-path: In-Reply-To: <20131002100224.GF17294@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Sender: "Linuxppc-dev" List-Id: kvm.vger.kernel.org On Wed, 2013-10-02 at 13:02 +0300, Gleb Natapov wrote: > Yes, I alluded to it in my email to Paul and Paolo asked also. How this > interface is disabled? Also hwrnd is MMIO in a host why guest needs to > use hypercall instead of emulating the device (in kernel or somewhere > else?). Migration will have to be dealt with one way or another, I suppose we will indeed need a qemu fallback. As for why hypercall instead of MMIO, well, you'd have to ask the folks who wrote the PAPR spec :-) It's specified as a hypercall and implemented as such in pHyp (PowerVM). The existing guests expect it that way. It might have to do with the required whitening done by the hypervisor (H_RANDOM output is supposed to be clean). It also abstracts us from the underlying HW implementation which could in theory change. > Another things is that on a host hwrnd is protected from > direct userspace access by virtue of been a device, but guest code (event > kernel mode) is userspace as far as hosts security model goes, so by > implementing this hypercall in a way that directly access hwrnd you > expose hwrnd to a userspace unconditionally. Why is this a good idea? Why would this be a bad idea ? Ben. > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html