[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] x86/hvm: Fix boot on systems where HVM isn't available
On 07/02/2022 08:29, Jan Beulich wrote: > On 05.02.2022 10:47, Roger Pau Monné wrote: >> On Fri, Feb 04, 2022 at 05:34:05PM +0000, Andrew Cooper wrote: >>> c/s 27a63cdac388 ("x86/HVM: convert remaining hvm_funcs hook invocations to >>> alt-call") went too far with dropping NULL function pointer checks. > Oh, I'm sorry, I should have noticed this. > >>> smp_callin() calls hvm_cpu_up() unconditionally. When the platform doesn't >>> support HVM, hvm_enable() exits without filling in hvm_funcs, after which >>> the >>> altcall pass nukes the (now unconditional) indirect call, causing: >>> >>> (XEN) ----[ Xen-4.17.0-10.18-d x86_64 debug=y Not tainted ]---- >>> (XEN) CPU: 1 >>> (XEN) RIP: e008:[<ffff82d04034bef5>] start_secondary+0x393/0x3b7 >>> (XEN) RFLAGS: 0000000000010086 CONTEXT: hypervisor >>> ... >>> (XEN) Xen code around <ffff82d04034bef5> (start_secondary+0x393/0x3b7): >>> (XEN) ff ff 8b 05 1b 84 17 00 <0f> 0b 0f ff ff 90 89 c3 85 c0 0f 84 db >>> fe ff ff >>> ... >>> (XEN) Xen call trace: >>> (XEN) [<ffff82d04034bef5>] R start_secondary+0x393/0x3b7 >>> (XEN) [<ffff82d0402000e2>] F __high_start+0x42/0x60 >>> >>> To make matters worse, __stop_this_cpu() calls hvm_cpu_down() >>> unconditionally >>> too, so what happen next is: >>> >>> (XEN) ----[ Xen-4.17.0-10.18-d x86_64 debug=y Not tainted ]---- >>> (XEN) CPU: 0 >>> (XEN) RIP: e008:[<ffff82d04034ab02>] __stop_this_cpu+0x12/0x3c >>> (XEN) RFLAGS: 0000000000010046 CONTEXT: hypervisor >>> ... >>> (XEN) Xen code around <ffff82d04034ab02> (__stop_this_cpu+0x12/0x3c): >>> (XEN) 48 89 e5 e8 8a 1d fd ff <0f> 0b 0f ff ff 90 0f 06 db e3 48 89 e0 >>> 48 0d ff >>> ... >>> (XEN) Xen call trace: >>> (XEN) [<ffff82d04034ab02>] R __stop_this_cpu+0x12/0x3c >>> (XEN) [<ffff82d04034ac15>] F smp_send_stop+0xdd/0xf8 >>> (XEN) [<ffff82d04034a229>] F machine_restart+0xa2/0x298 >>> (XEN) [<ffff82d04034a42a>] F >>> arch/x86/shutdown.c#__machine_restart+0xb/0x11 >>> (XEN) [<ffff82d04022fd15>] F smp_call_function_interrupt+0xbf/0xea >>> (XEN) [<ffff82d04034acc6>] F call_function_interrupt+0x35/0x37 >>> (XEN) [<ffff82d040331a70>] F do_IRQ+0xa3/0x6b5 >>> (XEN) [<ffff82d04039482a>] F common_interrupt+0x10a/0x120 >>> (XEN) [<ffff82d04031f649>] F __udelay+0x3a/0x51 >>> (XEN) [<ffff82d04034d5fb>] F __cpu_up+0x48f/0x734 >>> (XEN) [<ffff82d040203c2b>] F cpu_up+0x7d/0xde >>> (XEN) [<ffff82d0404543d3>] F __start_xen+0x200b/0x2618 >>> (XEN) [<ffff82d0402000ef>] F __high_start+0x4f/0x60 >>> >>> which recurses until hitting a stack overflow. The #DF handler, which >>> resets >>> its stack on each invocation, loops indefinitely. >>> >>> Reinstate the NULL function pointer checks for hvm_cpu_{up,down}(). >>> >>> Fixes: 27a63cdac388 ("x86/HVM: convert remaining hvm_funcs hook invocations >>> to alt-call") >>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> >> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> > Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> Thanks. > >>> --- >>> CC: Jan Beulich <JBeulich@xxxxxxxx> >>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx> >>> CC: Wei Liu <wl@xxxxxxx> >>> >>> RFC. Not tested yet on the imacted hardware. It's a Xeon PHI with another >>> werid thing in need of debugging. First boot is fine, while second >>> boot (loading microcode this time) has a problem with vmx. > Sounds not unfamiliar: My meanwhile oldish Romley needs to be cold- > booted for VMX to actually be usable (not locked) on APs. This is something which goes wrong as a consequence of loading microcode. >>> I wonder if we want to modify the callers to check for HVM being enabled, >>> rather than leaving the NULL pointer checks in a position where they're >>> liable >>> to be reaped again. >> What about adding a couple of comments to hvm_cpu_{up,down} to note >> they are called unconditionally regardless of whether HVM is present >> or not? > I second this as the perhaps better alternative: The S3 path is > similarly affected (and you may want to mention this in the > description), so this would mean up to 5 conditionals (at the > source level) instead of the just two you get away with here. Ok. I've added: /* Called in boot/resume paths. Must cope with no HVM support. */ and: /* Called in shutdown paths. Must cope with no HVM support. */ ~Andrew
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