From owner-freebsd-arm@freebsd.org Mon Sep 14 09:49:24 2015 Return-Path: Delivered-To: freebsd-arm@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 5A597A02C75 for ; Mon, 14 Sep 2015 09:49:24 +0000 (UTC) (envelope-from prvs=69285c8ee=Stefano.Stabellini@citrix.com) Received: from SMTP02.CITRIX.COM (smtp02.citrix.com [66.165.176.63]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "mail.citrix.com", Issuer "Verizon Public SureServer CA G14-SHA2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 14FCE159D for ; Mon, 14 Sep 2015 09:49:23 +0000 (UTC) (envelope-from prvs=69285c8ee=Stefano.Stabellini@citrix.com) X-IronPort-AV: E=Sophos;i="5.17,527,1437436800"; d="scan'208";a="303377731" Date: Mon, 14 Sep 2015 10:47:12 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Mark Rutland CC: Daniel Kiper , "devicetree@vger.kernel.org" , "linux-efi@vger.kernel.org" , "Ian.Campbell@citrix.com" , Konrad Rzeszutek Wilk , Stefano Stabellini , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "leif.lindholm@linaro.org" , "xen-devel@lists.xen.org" , "ard.biesheuvel@linaro.org" , "freebsd-arm@freebsd.org" , "matt.fleming@intel.com" , "christoffer.dall@linaro.org" , "jbeulich@suse.com" , Shannon Zhao , "julien.grall@citrix.com" , "peter.huangpeng@huawei.com" , "linux-arm-kernel@lists.infradead.org" , "shannon.zhao@linaro.org" Subject: Re: [PATCH] efi/libstub/fdt: Standardize the names of EFI stub parameters In-Reply-To: <20150914092518.GA10307@leverpostej> Message-ID: References: <20150910112418.GC29293@leverpostej> <20150910121514.GE29293@leverpostej> <20150910144938.GI29293@leverpostej> <20150910162302.GN29293@leverpostej> <20150911124643.GB4530@olila.local.net-space.pl> <20150911162559.GA8726@leverpostej> <20150912113655.GG4530@olila.local.net-space.pl> <20150914092518.GA10307@leverpostej> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA2 X-Mailman-Approved-At: Mon, 14 Sep 2015 11:23:01 +0000 X-BeenThere: freebsd-arm@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Porting FreeBSD to ARM processors." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 14 Sep 2015 09:49:24 -0000 On Mon, 14 Sep 2015, Mark Rutland wrote: > On Sat, Sep 12, 2015 at 12:36:55PM +0100, Daniel Kiper wrote: > > On Fri, Sep 11, 2015 at 05:25:59PM +0100, Mark Rutland wrote: > > > On Fri, Sep 11, 2015 at 01:46:43PM +0100, Daniel Kiper wrote: > > > > On Thu, Sep 10, 2015 at 05:23:02PM +0100, Mark Rutland wrote: > > > > [...] > > > > > > > What's troublesome with the boot services? > > > > > > > > > > What can't be simulated? > > > > > > > > How do you want to access bare metal EFI boot services from dom0 if they > > > > were shutdown long time ago before loading dom0 image? > > > > > > I don't want to. > > > > > > I asked "What can't be simulated?" because I assumed everything > > > necessary/mandatory could be simulated without needinng access to any > > > real EFI boot services. > > > > > > As far as I can see all that's necessary is to provide a compatible > > > interface. > > > > Could you be more precise what do you need? Please enumerate. UEFI spec has > > more than 2500 pages and I do not think that we need all stuff in dom0. > > > > > > What do you need from EFI boot services in dom0? > > > > > > The ability to call ExitBootServices() and SetVirtualAddressMap() on a > > > _virtual_ address map for _virtual_ services provided by the hypervisor. > > > > I am confused. Why do you need that? Please remember, EFI is owned and > > operated by Xen hypervisor. dom0 does not have direct access to EFI. > > Let's take a step back. > > My objection here is to passing the Dom0 kernel properties as if it were > booted with direct access to a full UEFI, then later fixing that up > (when Xen is detected and we apply its hypercall EFI implementation). > > If the kernel cannot use EFI natively, why pretend to the kernel that it > can? The hypercall implementation is _not_ EFI (though it provides > access to some services). > > The two ways I can see providing Dom0 with EFI services are: > > * Have Xen create shims for any services, in which any hypercalls live, > and pass these to the kernel with a virtual system table. This keeps > the interface to the kernel the same regardless of Xen. A not a fan of three-point estimates, so I am just going to say that "this looks like a lot of work". Also emulating services is known to be prone to errors. > * Have the kernel detect Xen EFI capability via Xen, without passing the > usual native EFI parameters. This can then be installed into the > kernel in a Xen-specific manner, and we know from the outset that > Xen-specific caveats apply. I prefer this approach by far. In the future we might have to move the xen_early_init call earlier (before ACPI and EFI Runtime Services get initialized). > As per my original email, I'm not against the renaming of the stub > parameters if we standardise the rest of the details, but I believe > that's orthogonal to the Xen Dom0 case.