On Fri, Oct 20, 2023 at 03:29:24AM +0000, Huang, Kai wrote:
> On Thu, 2023-10-05 at 16:14 +0300, Kirill A. Shutemov wrote:
> > ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> > kexec: target kernel won't be able to use more than one CPU.
> >
> > Zero out mailbox address in the ACPI MADT wakeup structure to indicate
> > that the mailbox is not usable.
> >
> > This is Linux-specific protocol and not reflected in ACPI spec.
> >
> > Booting the target kernel with signle CPU is enough to cover the most
> > common case for kexec -- kdump.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > ---
> > arch/x86/kernel/acpi/madt_wakeup.c | 17 +++++++++++++++++
> > 1 file changed, 17 insertions(+)
> >
> > diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> > index 15bdf10b1393..4e92d1d4a5fa 100644
> > --- a/arch/x86/kernel/acpi/madt_wakeup.c
> > +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> > @@ -9,6 +9,11 @@ static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> >
> > static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> > {
> > + if (!acpi_mp_wake_mailbox_paddr) {
> > + pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
> > + return -EOPNOTSUPP;
> > + }
> > +
> > /*
> > * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
> > *
> > @@ -78,6 +83,18 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> > /* Disable CPU onlining/offlining */
> > cpu_hotplug_not_supported();
> >
> > + /*
> > + * ACPI MADT doesn't allow to offline CPU after it got woke up.
> > + * It limits kexec: target kernel won't be able to use more than
> > + * one CPU.
> > + *
> > + * Zero out mailbox address in the ACPI MADT wakeup structure to
> > + * indicate that the mailbox is not usable.
>
> Nit:
>
> It is better to explicitly say that this will only impact the second kernel
> because the current kernel has already detected the mailbox address?
>
> Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> The acpi_wakeup_cpu() will use it to bring up secondary cpus.
>
> Zero out mailbox address in the ACPI MADT wakeup structure to
> indicate that the mailbox is not usable. This prevents the
> kexec()-ed kernel from reading a vaild mailbox, which in turn
> makes the kexec()-ed kernel only be able to use the boot CPU.
Okay. Looks good.
--
Kiryl Shutsemau / Kirill A. Shutemov
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