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[PATCHv2,11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

Message ID 20231020151242.1814-12-kirill.shutemov@linux.intel.com
State New
Headers
Series x86/tdx: Add kexec support |

Commit Message

Kirill A. Shutemov Oct. 20, 2023, 3:12 p.m. UTC 
  ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
kexec: the second kernel won't be able to use more than one CPU.

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.

Booting the second 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 | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

Comments

Kai Huang Oct. 24, 2023, 10:14 a.m. UTC | #1 
On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> kexec: the second kernel won't be able to use more than one CPU.
> 
> 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.
> 
> Booting the second 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>

Reviewed-by: Kai Huang <kai.huang@intel.com>
Kuppuswamy Sathyanarayanan Oct. 24, 2023, 1:59 p.m. UTC | #2 
On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> kexec: the second kernel won't be able to use more than one CPU.
> 
> 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.
> 
> Booting the second 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 | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> index 4bc1d5106afd..9bbe829737e7 100644
> --- a/arch/x86/kernel/acpi/madt_wakeup.c
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -13,6 +13,11 @@ 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 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
>  
>  	cpu_hotplug_disable_offlining();
>  
> +	/*
> +	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> +	 * It limits kexec: the second kernel won't be able to use more than
> +	 * one CPU.
> +	 *
> +	 * 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;

Is there any way to skip secondary CPU bring-up for kexec case instead of
returning error in ->wakeup_secondary_cpu_64()?

> +
>  	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
>  
>  	return 0;
Kirill A. Shutemov Oct. 27, 2023, 1:01 p.m. UTC | #3 
On Tue, Oct 24, 2023 at 06:59:58AM -0700, Kuppuswamy Sathyanarayanan wrote:
> 
> 
> On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> > ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> > kexec: the second kernel won't be able to use more than one CPU.
> > 
> > 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.
> > 
> > Booting the second 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 | 22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> > index 4bc1d5106afd..9bbe829737e7 100644
> > --- a/arch/x86/kernel/acpi/madt_wakeup.c
> > +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> > @@ -13,6 +13,11 @@ 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 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> >  
> >  	cpu_hotplug_disable_offlining();
> >  
> > +	/*
> > +	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
> > +	 * It limits kexec: the second kernel won't be able to use more than
> > +	 * one CPU.
> > +	 *
> > +	 * 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;
> 
> Is there any way to skip secondary CPU bring-up for kexec case instead of
> returning error in ->wakeup_secondary_cpu_64()?

I have not found a cleaner way. Do you have ideas?
diff mbox series

Patch

diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 4bc1d5106afd..9bbe829737e7 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -13,6 +13,11 @@  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 +83,23 @@  int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	cpu_hotplug_disable_offlining();
 
+	/*
+	 * ACPI MADT doesn't allow to offline CPU after it got woke up.
+	 * It limits kexec: the second kernel won't be able to use more than
+	 * one CPU.
+	 *
+	 * 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;