Messages in this thread | | | Date | Tue, 27 Jan 2009 07:35:02 -0500 | Subject | Re: unified percpu stuff | From | Brian Gerst <> |
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On Tue, Jan 27, 2009 at 2:24 AM, Jeremy Fitzhardinge <jeremy@goop.org> wrote: > Brian Gerst wrote: >> >> On Mon, Jan 26, 2009 at 8:12 PM, Jeremy Fitzhardinge <jeremy@goop.org> >> wrote: >> >>> >>> I'm really pleased to see the unified percpu stuff in the kernel, but >>> unfortunately its breaking Xen at the moment. >>> It looks like this is just a matter of initializing %gs properly in >>> xen_start_kernel. Is there any problem with me doing a load_gs_base(0) >>> somewhere early in xen_start_kernel (arch/x86/xen/enlighten.c)? >>> >> >> Some of the changes I did made the assumption that the percpu state is >> set up early in head_xx.S, which apparently is skipped for xen. Is >> there documentation anywhere for the xen bootstrap process? >> > > Not really. Its quite different from native because the guest kernel starts > up in protected/long mode with paging enabled, using a Xen-provided > pagetable. It means that most of the normal head.S stuff is redundant; the > kernel starts executing more or less exactly at xen_start_kernel (there's a > 2 instruction asm part which stashes away the Xen info pointer from %[re]si, > then jumps to xen_start_kernel). > >> Try this patch (untested): >> >> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c >> index bef941f..b90d061 100644 >> --- a/arch/x86/xen/enlighten.c >> +++ b/arch/x86/xen/enlighten.c >> @@ -1647,6 +1647,8 @@ asmlinkage void __init xen_start_kernel(void) >> have_vcpu_info_placement = 0; >> #endif >> >> + switch_to_new_gdt(); >> + >> xen_smp_init(); >> >> /* Get mfn list */ >> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c >> index 7735e3d..00d9265 100644 >> --- a/arch/x86/xen/smp.c >> +++ b/arch/x86/xen/smp.c >> @@ -235,6 +235,8 @@ cpu_initialize_context(unsigned int cpu, struct >> task_struct *idle) >> ctxt->user_regs.ss = __KERNEL_DS; >> #ifdef CONFIG_X86_32 >> ctxt->user_regs.fs = __KERNEL_PERCPU; >> +#else >> + ctxt->gs_base_kernel = per_cpu_offset(cpu); >> #endif >> ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle; >> ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */ >> > > Thanks, I'll try this out. > > BTW, does the initial cpu0 percpu area get reallocated and moved during > boot, or does cpu0 keep using the same memory forever?
It is reallocated in setup_per_cpu_areas().
-- Brian Gerst
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