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Date: Fri, 13 Mar 2020 09:26:58 +0100 From: Jürgen Groß <jgross@...e.com> To: Miroslav Benes <mbenes@...e.cz>, boris.ostrovsky@...cle.com, sstabellini@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com, jpoimboe@...hat.com Cc: x86@...nel.org, xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, jslaby@...e.cz Subject: Re: [RFC PATCH 2/2] x86/xen: Make the secondary CPU idle tasks reliable On 12.03.20 15:20, Miroslav Benes wrote: > The unwinder reports the secondary CPU idle tasks' stack on XEN PV as > unreliable, which affects at least live patching. > cpu_initialize_context() sets up the context of the CPU through > VCPUOP_initialise hypercall. After it is woken up, the idle task starts > in cpu_bringup_and_idle() function and its stack starts at the offset > right below pt_regs. The unwinder correctly detects the end of stack > there but it is confused by NULL return address in the last frame. > > RFC: I haven't found the way to teach the unwinder about the state of > the stack there. Thus the ugly hack using assembly. Similar to what > startup_xen() has got for boot CPU. > > It introduces objtool "unreachable instruction" warning just right after > the jump to cpu_bringup_and_idle(). It should show the idea what needs > to be done though, I think. Ideas welcome. > > Signed-off-by: Miroslav Benes <mbenes@...e.cz> > --- > arch/x86/xen/smp_pv.c | 3 ++- > arch/x86/xen/xen-head.S | 10 ++++++++++ > 2 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c > index 802ee5bba66c..6b88cdcbef8f 100644 > --- a/arch/x86/xen/smp_pv.c > +++ b/arch/x86/xen/smp_pv.c > @@ -53,6 +53,7 @@ static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 }; > static DEFINE_PER_CPU(struct xen_common_irq, xen_pmu_irq) = { .irq = -1 }; > > static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id); > +extern unsigned char asm_cpu_bringup_and_idle[]; > > static void cpu_bringup(void) > { Would adding this here work? + asm volatile (UNWIND_HINT(ORC_REG_UNDEFINED, 0, ORC_TYPE_CALL, 1)); Juergen
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