Re: [PATCH v2 10/18] x86, acpi: Try to find if SRAT is overrided earlier.

Toshi Kani
2013-08-02T01:20:24Z

On Thu, 2013-08-01 at 15:06 +0800, Tang Chen wrote:
> Linux cannot migrate pages used by the kernel due to the direct mapping
> (va = pa + PAGE_OFFSET), any memory used by the kernel cannot be hot-removed.
> So when using memory hotplug, we have to prevent the kernel from using
> hotpluggable memory.
>
> The ACPI table SRAT (System Resource Affinity Table) contains info to specify
> which memory is hotpluggble. After SRAT is parsed, we are aware of which
> memory is hotpluggable.
>
> At the early time when system is booting, SRAT has not been parsed. The boot
> memory allocator memblock will allocate any memory to the kernel. So we need
> SRAT parsed before memblock starts to work.
>
> In this patch, we are going to parse SRAT earlier, right after memblock is ready.
>
> Generally speaking, tables such as SRAT are provided by firmware. But
> ACPI_INITRD_TABLE_OVERRIDE functionality allows users to customize their own
> tables in initrd, and override the ones from firmware. So if we want to parse
> SRAT earlier, we also need to do SRAT override earlier.
>
> First, we introduce early_acpi_override_srat() to check if SRAT will be overridden
> from initrd.
>
> Second, we introduce find_hotpluggable_memory() to reserve hotpluggable memory,
> which will firstly call early_acpi_override_srat() to find out which memory is
> hotpluggable in the override SRAT.
>
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
> ---
> arch/x86/kernel/setup.c | 10 +++++++
> drivers/acpi/osl.c | 58 ++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 14 ++++++++-
> include/linux/memory_hotplug.h | 2 +
> mm/memory_hotplug.c | 25 ++++++++++++++++-
> 5 files changed, 106 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index c8f5d1a..8b1bddd 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1060,6 +1060,16 @@ void __init setup_arch(char **cmdline_p)
> /* Initialize ACPI root table */
> acpi_root_table_init();
>
> +#ifdef CONFIG_ACPI_NUMA
> + /*
> + * Linux kernel cannot migrate kernel pages, as a result, memory used
> + * by the kernel cannot be hot-removed. Find and mark hotpluggable
> + * memory in memblock to prevent memblock from allocating hotpluggable
> + * memory for the kernel.
> + */
> + find_hotpluggable_memory();
> +#endif
> +
> /*
> * The EFI specification says that boot service code won't be called
> * after ExitBootServices(). This is, in fact, a lie.
> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> index 8df8a93..d0b687c 100644
> --- a/drivers/acpi/osl.c
> +++ b/drivers/acpi/osl.c
> @@ -48,6 +48,7 @@
>
> #include <asm/io.h>
> #include <asm/uaccess.h>
> +#include <asm/setup.h>
>
> #include <acpi/acpi.h>
> #include <acpi/acpi_bus.h>
> @@ -631,6 +632,63 @@ int __init acpi_invalid_table(struct cpio_data *file,
> return 0;
> }
>
> +#ifdef CONFIG_ACPI_NUMA
> +/*******************************************************************************
> + *
> + * FUNCTION: early_acpi_override_srat
> + *
> + * RETURN: Phys addr of SRAT on success, 0 on error.
> + *
> + * DESCRIPTION: Try to get the phys addr of SRAT in initrd.
> + * The ACPI_INITRD_TABLE_OVERRIDE procedure is able to use tables
> + * in initrd file to override the ones provided by firmware. This
> + * function checks if there is a SRAT in initrd at early time. If
> + * so, return the phys addr of the SRAT.
> + *
> + ******************************************************************************/
> +phys_addr_t __init early_acpi_override_srat(void)
> +{
> + int i;
> + u32 length;
> + long offset;
> + void *ramdisk_vaddr;
> + struct acpi_table_header *table;
> + struct cpio_data file;
> + unsigned long map_step = NR_FIX_BTMAPS << PAGE_SHIFT;
> + phys_addr_t ramdisk_image = get_ramdisk_image();
> + char cpio_path[32] = "kernel/firmware/acpi/";

Don't you need to check if ramdisk is present before parsing the table?
You may need something like:

if (!ramdisk_image || !get_ramdisk_size())
return 0;

> +
> + /* Try to find if SRAT is overrided */

overrided -> overridden

> + for (i = 0; i < ACPI_OVERRIDE_TABLES; i++) {
> + ramdisk_vaddr = early_ioremap(ramdisk_image, map_step);
> +
> + file = find_cpio_data(cpio_path, ramdisk_vaddr,
> + map_step, &offset);
> + if (!file.data) {
> + early_iounmap(ramdisk_vaddr, map_step);
> + return 0;
> + }
> +
> + table = file.data;
> + length = table->length;
> +
> + if (acpi_invalid_table(&file, cpio_path, ACPI_SIG_SRAT)) {
> + ramdisk_image += offset;
> + early_iounmap(ramdisk_vaddr, map_step);
> + continue;
> + }
> +
> + /* Found SRAT */
> + early_iounmap(ramdisk_vaddr, map_step);
> + ramdisk_image = ramdisk_image + offset - length;
> +
> + break;
> + }
> +
> + return ramdisk_image;

Doesn't this function return a physical address regardless of SRAT if a
ramdisk is present?

Thanks,
-Toshi