diff mbox series

[12/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

Message ID 20231005131402.14611-13-kirill.shutemov@linux.intel.com
State New
Headers
Series x86/tdx: Add kexec support |

Commit Message

Kirill A. Shutemov Oct. 5, 2023, 1:14 p.m. UTC 
  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@linux.intel.com>
---
 arch/x86/kernel/acpi/madt_wakeup.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Comments

Kai Huang Oct. 20, 2023, 3:29 a.m. UTC | #1 
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@linux.intel.com>
> ---
>  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. 

> +	 *
> +	 * This is Linux-specific protocol and not reflected in ACPI spec.
> +	 */
> +	mp_wake->base_address = 0;
> + 
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
>  	return 0;
Kirill A. Shutemov Oct. 20, 2023, 9:29 a.m. UTC | #2 
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@linux.intel.com>
> > ---
> >  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.
diff mbox series

Patch

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.
+	 *
+	 * This is Linux-specific protocol and not reflected in ACPI spec.
+	 */
+	mp_wake->base_address = 0;
+
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
 
 	return 0;