Re: [PATCH v7 1/8] efi: Export boot-services code and data as debugfs-blobs

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Fri, 4 Oct 2019 at 16:51, Hans de Goede <hdegoede@redhat.com> wrote:
>
> Sometimes it is useful to be able to dump the efi boot-services code and
> data. This commit adds these as debugfs-blobs to /sys/kernel/debug/efi,
> but only if efi=debug is passed on the kernel-commandline as this requires
> not freeing those memory-regions, which costs 20+ MB of RAM.
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
> Changes in v5:
> -Rename the EFI_BOOT_SERVICES flag to EFI_PRESERVE_BS_REGIONS
>
> Changes in v4:
> -Add new EFI_BOOT_SERVICES flag and use it to determine if the boot-services
>  memory segments are available (and thus if it makes sense to register the
>  debugfs bits for them)
>
> Changes in v2:
> -Do not call pr_err on debugfs call failures
> ---
>  arch/x86/platform/efi/efi.c    |  1 +
>  arch/x86/platform/efi/quirks.c |  4 +++
>  drivers/firmware/efi/efi.c     | 53 ++++++++++++++++++++++++++++++++++
>  include/linux/efi.h            |  1 +
>  4 files changed, 59 insertions(+)
>
> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index c202e1b07e29..847730f7e74b 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -232,6 +232,7 @@ int __init efi_memblock_x86_reserve_range(void)
>              efi.memmap.desc_version);
>
>         memblock_reserve(pmap, efi.memmap.nr_map * efi.memmap.desc_size);
> +       set_bit(EFI_PRESERVE_BS_REGIONS, &efi.flags);

Should we add a Kconfig symbol to opt into this behavior [set by the
driver in question], instead of always preserving all boot services
regions on all x86 systems?

>
>         return 0;
>  }
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index 3b9fd679cea9..fab12ebf0ada 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -411,6 +411,10 @@ void __init efi_free_boot_services(void)
>         int num_entries = 0;
>         void *new, *new_md;
>
> +       /* Keep all regions for /sys/kernel/debug/efi */
> +       if (efi_enabled(EFI_DBG))
> +               return;
> +
>         for_each_efi_memory_desc(md) {
>                 unsigned long long start = md->phys_addr;
>                 unsigned long long size = md->num_pages << EFI_PAGE_SHIFT;
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 8d3e778e988b..abba49c4c46d 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -17,6 +17,7 @@
>  #include <linux/kobject.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
> +#include <linux/debugfs.h>
>  #include <linux/device.h>
>  #include <linux/efi.h>
>  #include <linux/of.h>
> @@ -314,6 +315,55 @@ static __init int efivar_ssdt_load(void)
>  static inline int efivar_ssdt_load(void) { return 0; }
>  #endif
>
> +#ifdef CONFIG_DEBUG_FS
> +
> +#define EFI_DEBUGFS_MAX_BLOBS 32
> +
> +static struct debugfs_blob_wrapper debugfs_blob[EFI_DEBUGFS_MAX_BLOBS];
> +
> +static void __init efi_debugfs_init(void)
> +{
> +       struct dentry *efi_debugfs;
> +       efi_memory_desc_t *md;
> +       char name[32];
> +       int type_count[EFI_BOOT_SERVICES_DATA + 1] = {};
> +       int i = 0;
> +
> +       efi_debugfs = debugfs_create_dir("efi", NULL);
> +       if (IS_ERR_OR_NULL(efi_debugfs))
> +               return;
> +
> +       for_each_efi_memory_desc(md) {
> +               switch (md->type) {
> +               case EFI_BOOT_SERVICES_CODE:
> +                       snprintf(name, sizeof(name), "boot_services_code%d",
> +                                type_count[md->type]++);
> +                       break;
> +               case EFI_BOOT_SERVICES_DATA:
> +                       snprintf(name, sizeof(name), "boot_services_data%d",
> +                                type_count[md->type]++);
> +                       break;
> +               default:
> +                       continue;
> +               }
> +
> +               debugfs_blob[i].size = md->num_pages << EFI_PAGE_SHIFT;
> +               debugfs_blob[i].data = memremap(md->phys_addr,
> +                                               debugfs_blob[i].size,
> +                                               MEMREMAP_WB);
> +               if (!debugfs_blob[i].data)
> +                       continue;
> +
> +               debugfs_create_blob(name, 0400, efi_debugfs, &debugfs_blob[i]);
> +               i++;
> +               if (i == EFI_DEBUGFS_MAX_BLOBS)
> +                       break;
> +       }
> +}
> +#else
> +static inline void efi_debugfs_init(void) {}
> +#endif
> +
>  /*
>   * We register the efi subsystem with the firmware subsystem and the
>   * efivars subsystem with the efi subsystem, if the system was booted with
> @@ -370,6 +420,9 @@ static int __init efisubsys_init(void)
>                 goto err_remove_group;
>         }
>
> +       if (efi_enabled(EFI_DBG) && efi_enabled(EFI_PRESERVE_BS_REGIONS))
> +               efi_debugfs_init();
> +
>         return 0;
>
>  err_remove_group:
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index bd3837022307..2a30a1bd8bdf 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1202,6 +1202,7 @@ extern int __init efi_setup_pcdp_console(char *);
>  #define EFI_DBG                        8       /* Print additional debug info at runtime */
>  #define EFI_NX_PE_DATA         9       /* Can runtime data regions be mapped non-executable? */
>  #define EFI_MEM_ATTR           10      /* Did firmware publish an EFI_MEMORY_ATTRIBUTES table? */
> +#define EFI_PRESERVE_BS_REGIONS        11      /* Are EFI boot-services memory segments available? */
>
>  #ifdef CONFIG_EFI
>  /*
> --
> 2.23.0
>