From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759095AbcAUIiq (ORCPT ); Thu, 21 Jan 2016 03:38:46 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:58468 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759077AbcAUIio (ORCPT ); Thu, 21 Jan 2016 03:38:44 -0500 X-IronPort-AV: E=Sophos;i="5.22,324,1449532800"; d="scan'208";a="332956739" Subject: Re: [RFC v1 4/8] x86/init: add linker table support To: "Luis R. Rodriguez" , Konrad Rzeszutek Wilk , Boris Ostrovsky , Stefano Stabellini References: <1450217797-19295-1-git-send-email-mcgrof@do-not-panic.com> <1450217797-19295-5-git-send-email-mcgrof@do-not-panic.com> <20160120210014.GF4769@char.us.oracle.com> CC: "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Rusty Russell , Andy Lutomirski , , Juergen Gross , Jan Beulich , , Andrey Ryabinin , , , , , Mauro Carvalho Chehab , Valentin Rothberg , Peter Senna Tschudin , X86 ML , "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" From: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= X-Enigmail-Draft-Status: N1110 Message-ID: <56A0990C.9090601@citrix.com> Date: Thu, 21 Jan 2016 09:38:36 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org El 20/01/16 a les 22.33, Luis R. Rodriguez ha escrit: > On Wed, Jan 20, 2016 at 1:00 PM, Konrad Rzeszutek Wilk > wrote: >>> +static bool x86_init_fn_supports_subarch(struct x86_init_fn *fn) >>> +{ >>> + if (!fn->supp_hardware_subarch) { >>> + pr_err("Init sequence fails to declares any supported subarchs: %pF\n", fn->early_init); >>> + WARN_ON(1); >>> + } >>> + if (BIT(boot_params.hdr.hardware_subarch) & fn->supp_hardware_subarch) >>> + return true; >>> + return false; >>> +} >> >> So the logic for this working is that boot_params.hdr.hardware_subarch >> >> And the macros define two: BIT(X86_SUBARCH_PC) or BIT(X86_SUBARCH_XEN). >> >> But hardware_subarch by default is set to zero. Which means if GRUB2, PXELinux, Xen multiboot1 >> don't set it - then the X86_SUBARCH_PC is choosen right? >> >> 1 << 0 & 1 << X86_SUBARCH_PC (which is zero). >> >> For this to nicely work with Xen it ought to do this: >> >> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c >> index 993b7a7..6cf9afd 100644 >> --- a/arch/x86/xen/enlighten.c >> +++ b/arch/x86/xen/enlighten.c >> @@ -1676,6 +1676,7 @@ asmlinkage __visible void __init xen_start_kernel(void) >> boot_params.hdr.ramdisk_image = initrd_start; >> boot_params.hdr.ramdisk_size = xen_start_info->mod_len; >> boot_params.hdr.cmd_line_ptr = __pa(xen_start_info->cmd_line); >> + boot_params.hdr.hardware_subarch = X86_SUBARCH_XEN; >> >> if (!xen_initial_domain()) { >> add_preferred_console("xenboot", 0, NULL); >> >> >> ? > > That's correct for PV and PVH, likewise when qemu is required for HVM > qemu could set it. I have the qemu change done but that should only > cover HVM. A common place to set this as well could be the hypervisor, > but currently the hypervisor doesn't set any boot_params, instead a > generic struct is passed and the kernel code (for any OS) is expected > to interpret this and then set the required values for the OS in the > init path. Long term though if we wanted to merge init further one way > could be to have the hypervisor just set the zero page cleanly for the > different modes. If we needed more data other than the > hardware_subarch we also have the hardware_subarch_data, that's a u64 > , and how that is used would be up to the subarch. In Xen's case it > could do what it wants with it. That would still mean perhaps defining > as part of a Xen boot protocol a place where xen specific code can > count on finding more Xen data passed by the hypervisor, the > xen_start_info. That is, if we wanted to merge init paths this is > something to consider. > > One thing I considered on the question of who should set the zero page > for Xen with the prospect of merging inits, or at least this subarch > for both short term and long term are the obvious implications in > terms of hypervisor / kernel / qemu combination requirements if the > subarch is needed. Having it set in the kernel is an obvious immediate > choice for PV / PVH but it means we can't merge init paths completely > (down to asm inits), we'd still be able to merge some C init paths > though, the first entry would still be different. Having the zero page > set on the hypervisor would go long ways but it would mean a > hypervisor change required. I don't think the hypervisor should be setting Linux specific boot related parameters, the boot ABI should be OS agnostic. IMHO, a small shim should be added to Linux in order to set what Linux requires when entering from a Xen entry point. Roger.