From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [PATCH 11/19] KVM: PPC: Book3S HV: add support for the XIVE native exploitation mode hcalls Date: Thu, 24 Jan 2019 08:23:52 +1100 Message-ID: <5272c33a70456503c9f72d6735c8567a070dcb7c.camel@kernel.crashing.org> References: <20190107184331.8429-1-clg@kaod.org> <20190107184331.8429-12-clg@kaod.org> <20190122052346.GF15124@blackberry> <3ada7c25-c671-32d2-4c91-dd7e84c29e48@kaod.org> <20190123102603.GA29826@blackberry> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, David Gibson To: Paul Mackerras , =?ISO-8859-1?Q?C=E9dric?= Le Goater Return-path: In-Reply-To: <20190123102603.GA29826@blackberry> 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, 2019-01-23 at 21:26 +1100, Paul Mackerras wrote: > If H_INT_ESB is only used for LSIs, then is a guest going to be using > it at all? *emulated* LSIs, ie LSIs coming from emulated devices. It will depends in practice of what kind of emulated device you put in your guest. We need that because under the hood, we send a XIVE MSI, so we need to be notified of the EOI so we can resend if the emulated LSI is still asserted. > My understanding was that with XIVE, only a small number > of interrupts that are to do with system management functions are > LSIs; all of the interrupts relating to PCI-e devices are MSIs. So do > we actually have a real high-frequency use case for LSIs in a guest? > > For now I would prefer that you remove all the real-mode hcall > handlers. We can add them later if we get performance data showing > that they are needed. > > Regarding whether or not to have a given hcall handler in the kernel > at all - if there is for example an hcall which is just called once > on guest startup, and its function is just to provide information to > the guest, and QEMU has that information, then why not have that hcall > implemented by QEMU? Are any of the hcalls like that? > > For example, if H_INT_GET_SOURCE_INFO was implemented in QEMU, could > we then remove the VC_BASE thing from the xive device? Ben.