Messages in this thread | | | Subject | Re: [PATCH v3 0/5] x86/apic: Fix restoring boot irq mode in reboot and kexec/kdump | From | Dou Liyang <> | Date | Mon, 12 Feb 2018 16:58:33 +0800 |
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Hi Eric,
At 02/12/2018 01:11 PM, Eric W. Biederman wrote: > Dou Liyang <douly.fnst@cn.fujitsu.com> writes: > >> Hi all, >> >> One thing confused me. >> >> The disconnect_bsp_APIC() may restore the interrupt delivery mode into >> virtual wire mode. it uses the vector F as the spurious interrput, But, >> IMO, using the vector 0xFF(SPURIOUS_APIC_VECTOR) may more suitable and >> will give us more detail. Why the disconnect_bsp_APIC() use vector F >> here? > > I would say this needs a documentation search before changing this. > > This code originates in: > 208fb93162d5 ("[PATCH] kexec: x86_64: restore apic virtual wire mode on shutdown") > > The example in the Multi-Processor Specification v1.4 shows setting > up the SPIV to vector 0x0f. > Thanks for your detailed explanation, I found the example A-1 in this spec.
> I don't know what is canonical and what will interact best with DOS, > and that erra of setup. The vector 0x0f seems an odd choice as > it is below 0x20 putting it in the range of vectors that are > reserved for processor exceptions. > > The constant SPURIOUS_APIC_VECTOR is definitely not something we want > to be using at this point as that is a linux specific setting and used > when Linux is up and running. So it is completely inapplicable. > > This is all about restoring how the apics were configured at boot time > so it may be appropriate to copy and store this value, if it was not > architectural. > > At a practical level at this point I suspect we are ok as the setting > of the SPIV this way has not caused any known problems in the last > decade. If someone wants to dig through the archtectural documents > and the real world practice and find a better value and explain the > change I would not oppose it.
Indeed, I understand.
Thanks, dou
> > All I know for certain is using the constant SPURIOUS_APIC_VECTOR > is completely inappropriate (as that constant is about how linux uses > vectors) and thus the patch below is wrong. > >> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c >> index 25ddf02598d2..550deaad6a9a 100644 >> --- a/arch/x86/kernel/apic/apic.c >> +++ b/arch/x86/kernel/apic/apic.c >> @@ -2130,7 +2130,7 @@ void disconnect_bsp_APIC(int virt_wire_setup) >> value = apic_read(APIC_SPIV); >> value &= ~APIC_VECTOR_MASK; >> value |= APIC_SPIV_APIC_ENABLED; >> - value |= 0xf; >> + value |= SPURIOUS_APIC_VECTOR; >> apic_write(APIC_SPIV, value); >> >> if (!virt_wire_setup) { >> > > Eric > > >
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