Messages in this thread | | | From | (Eric W. Biederman) | Date | Tue, 13 Feb 2018 11:44:47 -0600 | Subject | Re: [PATCH v3 2/5] x86/apic: Fix restoring boot irq mode in reboot and kexec/kdump |
| |
Baoquan He <bhe@redhat.com> writes:
> Hi Eric, > > On 02/11/18 at 09:08pm, Eric W. Biederman wrote: >> Baoquan He <bhe@redhat.com> writes: >> >> > This is a regression fix. >> > >> > Before, to fix erratum AVR31, commit 522e66464467 ("x86/apic: Disable >> > I/O APIC before shutdown of the local APIC") moved lapic_shutdown() >> > calling after disable_IO_APIC(). This introdued a regression. The >> > root cause is that disable_IO_APIC() not only clears IO_APIC, also >> > restore boot irq mode by setting LAPIC/APIC/IMCR, lapic_shutdown() >> > after disable_IO_APIC() will disable LAPIC and ruin the possible >> > virtual wire mode setting which the code has been trying to do all >> > along. >> > To fix this, just break down disable_IO_APIC(), then call >> > clear_IO_APIC() to stop IO_APIC where disable_IO_APIC() was called, >> > and call restore_boot_irq_mode() to restore boot irq mode before >> > reboot or kexec/kdump jump. >> >> Two things here. >> a) This is missing a fixes tag and a CC stable. >> b) What makes your change to the KEXEC_JUMP code path safe? >> Have the lapic and ioapic already been shut down? >> >> The KEXEC_JUMP changes to machine_kexec_32.c and machine_kexec_64.c >> either need to be documented in the change long why they are safe >> so that this change becomes obviously safe and correct. > > Re-read the code, I have to admit I didn't check the KEXEC_JUMP code > path carefully. > > kernel_kexec() { > if (kexec_image->preserve_context) { > ... > freeze_processes(); > ... > disable_nonboot_cpus(); > ... > > else { > ... > machine_shutdown(); > ... > } > machine_kexec(kexec_image); > ... > } > > --machine_shutdown() > --native_machine_shutdown() > --disable_IO_APIC() > --lapic_shutdown() > > machine_kexec() { > ... > if (image->preserve_context) { > disable_IO_APIC(); > } > ... > } > > KEXEC_JUMP code path is different than kexec/kdump, it doesn't call > lapic_shutdown() before jump. So commit 522e66464467 > ("x86/apic: Disable I/O APIC before shutdown of the local APIC") didn't > impact it. And here I break down disable_IO_APIC() and change to only > call restore_boot_irq_mode() to make a possible danger. I am not an > expert on KEXEC_JUMP, and don't know how to test it, so will keep the > code implementation consistent as before. For now, I plan to change it > as below if you don't object. As you pointed out, I will describe this > in patch log. > > diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c > index 1f790cf9d38f..cb0c2d0a4c99 100644 > --- a/arch/x86/kernel/machine_kexec_64.c > +++ b/arch/x86/kernel/machine_kexec_64.c > @@ -297,7 +297,7 @@ void machine_kexec(struct kimage *image) > * one form or other. kexec jump path also need > * one. > */ > - disable_IO_APIC(); > + clear_IO_APIC(); > + restore_boot_irq_mode(); > #endif > } > >
Let me give a very concrete suggestion: Patch 1) Replace "disable_IO_APIC();" with "clear_IO_APIC(); restore_boot_irq_mode();" Patch 2) Move restore_boot_irq_mode(); to fix the regression.
I think that will be a slightly shorter patch sequence than what you are dealing with and one that is slightly easier to read.
We need to sort out KEXEC_JUMP but that is something for another time.
Eric
| |