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SubjectRe: [PATCH v5 03/22] cc_platform: Add new attribute to prevent ACPI memory hotplug
On Wed, Jun 22, 2022 at 1:16 PM Kai Huang <kai.huang@intel.com> wrote:
>
> Platforms with confidential computing technology may not support ACPI
> memory hotplug when such technology is enabled by the BIOS. Examples
> include Intel platforms which support Intel Trust Domain Extensions
> (TDX).
>
> If the kernel ever receives ACPI memory hotplug event, it is likely a
> BIOS bug. For ACPI memory hot-add, the kernel should speak out this is
> a BIOS bug and reject the new memory. For hot-removal, for simplicity
> just assume the kernel cannot continue to work normally, and just BUG().
>
> Add a new attribute CC_ATTR_ACPI_MEMORY_HOTPLUG_DISABLED to indicate the
> platform doesn't support ACPI memory hotplug, so that kernel can handle
> ACPI memory hotplug events for such platform.
>
> In acpi_memory_device_{add|remove}(), add early check against this
> attribute and handle accordingly if it is set.
>
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> ---
> drivers/acpi/acpi_memhotplug.c | 23 +++++++++++++++++++++++
> include/linux/cc_platform.h | 10 ++++++++++
> 2 files changed, 33 insertions(+)
>
> diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
> index 24f662d8bd39..94d6354ea453 100644
> --- a/drivers/acpi/acpi_memhotplug.c
> +++ b/drivers/acpi/acpi_memhotplug.c
> @@ -15,6 +15,7 @@
> #include <linux/acpi.h>
> #include <linux/memory.h>
> #include <linux/memory_hotplug.h>
> +#include <linux/cc_platform.h>
>
> #include "internal.h"
>
> @@ -291,6 +292,17 @@ static int acpi_memory_device_add(struct acpi_device *device,
> if (!device)
> return -EINVAL;
>
> + /*
> + * If the confidential computing platform doesn't support ACPI
> + * memory hotplug, the BIOS should never deliver such event to
> + * the kernel. Report ACPI CPU hot-add as a BIOS bug and ignore
> + * the memory device.
> + */
> + if (cc_platform_has(CC_ATTR_ACPI_MEMORY_HOTPLUG_DISABLED)) {

Same comment as for the acpi_processor driver: this will affect the
initialization too and it would be cleaner to reset the
.hotplug.enabled flag of the scan handler.

> + dev_err(&device->dev, "[BIOS bug]: Platform doesn't support ACPI memory hotplug. New memory device ignored.\n");
> + return -EINVAL;
> + }
> +
> mem_device = kzalloc(sizeof(struct acpi_memory_device), GFP_KERNEL);
> if (!mem_device)
> return -ENOMEM;
> @@ -334,6 +346,17 @@ static void acpi_memory_device_remove(struct acpi_device *device)
> if (!device || !acpi_driver_data(device))
> return;
>
> + /*
> + * The confidential computing platform is broken if ACPI memory
> + * hot-removal isn't supported but it happened anyway. Assume
> + * it is not guaranteed that the kernel can continue to work
> + * normally. Just BUG().
> + */
> + if (cc_platform_has(CC_ATTR_ACPI_CPU_HOTPLUG_DISABLED)) {
> + dev_err(&device->dev, "Platform doesn't support ACPI memory hotplug. BUG().\n");
> + BUG();
> + }
> +
> mem_device = acpi_driver_data(device);
> acpi_memory_remove_memory(mem_device);
> acpi_memory_device_free(mem_device);
> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
> index 9ce9256facc8..b831c24bd7f6 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -93,6 +93,16 @@ enum cc_attr {
> * Examples include TDX platform.
> */
> CC_ATTR_ACPI_CPU_HOTPLUG_DISABLED,
> +
> + /**
> + * @CC_ATTR_ACPI_MEMORY_HOTPLUG_DISABLED: ACPI memory hotplug is
> + * not supported.
> + *
> + * The platform/os does not support ACPI memory hotplug.
> + *
> + * Examples include TDX platform.
> + */
> + CC_ATTR_ACPI_MEMORY_HOTPLUG_DISABLED,
> };
>
> #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
> --
> 2.36.1
>

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