Date: Fri, 11 Sep 2015 17:36:05 +0100 From: Mark Rutland <mark.rutland@arm.com> To: Jan Beulich <JBeulich@suse.com> Cc: "Ian.Campbell@citrix.com" <Ian.Campbell@citrix.com>, "julien.grall@citrix.com" <julien.grall@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org>, "peter.huangpeng@huawei.com" <peter.huangpeng@huawei.com>, Shannon Zhao <zhaoshenglong@huawei.com>, "matt.fleming@intel.com" <matt.fleming@intel.com>, "ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>, "christoffer.dall@linaro.org" <christoffer.dall@linaro.org>, "leif.lindholm@linaro.org" <leif.lindholm@linaro.org>, "shannon.zhao@linaro.org" <shannon.zhao@linaro.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, "daniel.kiper@oracle.com" <daniel.kiper@oracle.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>, "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org> Subject: Re: [PATCH] efi/libstub/fdt: Standardize the names of EFI stub parameters Message-ID: <20150911163605.GC8726@leverpostej> In-Reply-To: <55F1B89802000078000A1C9B@prv-mh.provo.novell.com> References: <1441874516-11364-1-git-send-email-zhaoshenglong@huawei.com> <20150910095208.GA29293@leverpostej> <alpine.DEB.2.02.1509101116580.2672@kaball.uk.xensource.com> <20150910112418.GC29293@leverpostej> <alpine.DEB.2.02.1509101223580.2672@kaball.uk.xensource.com> <55F199DD02000078000A1B1E@prv-mh.provo.novell.com> <20150910145331.GJ29293@leverpostej> <55F1B89802000078000A1C9B@prv-mh.provo.novell.com>
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> >> Considering that the EFI support is just for Dom0, and Dom0 (at > >> the time) had to be PV anyway, it was the more natural solution to > >> expose the interface via hypercalls, the more that this allows better > >> control over what is and primarily what is not being exposed to > >> Dom0. With the wrapper approach we'd be back to the same > >> problem (discussed elsewhere) of which EFI version to surface: The > >> host one would impose potentially missing extensions, while the > >> most recent hypervisor known one might imply hiding valuable > >> information from Dom0. Plus there are incompatible changes like > >> the altered meaning of EFI_MEMORY_WP in 2.5. > > > > I'm not sure I follow how hypercalls solve any impedance mismatch here; > > you're still expecting Dom0 to call up to Xen in order to perform calls, > > and all I suggested was a different location for those hypercalls. > > > > If Xen is happy to make such calls blindly, why does it matter if the > > hypercall was in the kernel binary or an external shim? > > Because there could be new entries in SystemTable->RuntimeServices > (expected and blindly but validly called by the kernel). Even worse > (because likely harder to deal with) would be new fields in other > structures. Any of these could cause Xen to blow up, while Xen could always provide a known-safe (but potentially sub-optimal) view to the kernel by default. > > Incompatible changes are a spec problem regardless of how this is > > handled. > > Not necessarily - we don't expose the memory map (we'd have to > if we were to mimic EFI for Dom0), and hence the mentioned issue > doesn't exist in our model. We have to expose _some_ memory map, so I don't follow this point. Mark.
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