[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC v1 4/8] x86/init: add linker table support
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 > <konrad.wilk@xxxxxxxxxx> 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. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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