Date: Mon, 14 Sep 2015 10:47:12 +0100 From: Stefano Stabellini <stefano.stabellini@eu.citrix.com> To: Mark Rutland <mark.rutland@arm.com> Cc: Daniel Kiper <daniel.kiper@oracle.com>, "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>, "Ian.Campbell@citrix.com" <Ian.Campbell@citrix.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "leif.lindholm@linaro.org" <leif.lindholm@linaro.org>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, "ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org>, "matt.fleming@intel.com" <matt.fleming@intel.com>, "christoffer.dall@linaro.org" <christoffer.dall@linaro.org>, "jbeulich@suse.com" <jbeulich@suse.com>, Shannon Zhao <zhaoshenglong@huawei.com>, "julien.grall@citrix.com" <julien.grall@citrix.com>, "peter.huangpeng@huawei.com" <peter.huangpeng@huawei.com>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "shannon.zhao@linaro.org" <shannon.zhao@linaro.org> Subject: Re: [PATCH] efi/libstub/fdt: Standardize the names of EFI stub parameters Message-ID: <alpine.DEB.2.02.1509141043520.2672@kaball.uk.xensource.com> In-Reply-To: <20150914092518.GA10307@leverpostej> References: <20150910112418.GC29293@leverpostej> <alpine.DEB.2.02.1509101223580.2672@kaball.uk.xensource.com> <20150910121514.GE29293@leverpostej> <alpine.DEB.2.02.1509101429480.2672@kaball.uk.xensource.com> <20150910144938.GI29293@leverpostej> <alpine.DEB.2.02.1509101655020.2672@kaball.uk.xensource.com> <20150910162302.GN29293@leverpostej> <20150911124643.GB4530@olila.local.net-space.pl> <20150911162559.GA8726@leverpostej> <20150912113655.GG4530@olila.local.net-space.pl> <20150914092518.GA10307@leverpostej>
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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.
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