Re: [PATCH v3 1/5] efi: Export boot-services code and data as debugfs-blobs

[Hans de Goede]

Hi,

On 16-04-18 10:23, Ard Biesheuvel wrote:
> Hallo Hans,
>
> On 8 April 2018 at 19:40, Hans de Goede <hdegoede@xxxxxxxxxx> 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.
> >
> > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > ---
> > Changes in v2:
> > -Do not call pr_err on debugfs call failures
> > ---
> >   arch/x86/platform/efi/quirks.c |  4 +++
> >   drivers/firmware/efi/efi.c     | 53 ++++++++++++++++++++++++++++++++++
> >   2 files changed, 57 insertions(+)
> >
> > diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> > index 5b513ccffde4..0f968c7bcfec 100644
> > --- a/arch/x86/platform/efi/quirks.c
> > +++ b/arch/x86/platform/efi/quirks.c
> > @@ -374,6 +374,10 @@ 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 cd42f66a7c85..10c896e8b82b 100644
> > --- a/drivers/firmware/efi/efi.c
> > +++ b/drivers/firmware/efi/efi.c
> > @@ -18,6 +18,7 @@
> >   #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>
> > @@ -316,6 +317,55 @@ 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
> > @@ -360,6 +410,9 @@ static int __init efisubsys_init(void)
> >                  goto err_remove_group;
> >          }
> >
> > +       if (efi_enabled(EFI_DBG))
> > +               efi_debugfs_init();
> > +
>
> This doesn't really make any sense on non-x86. The boot services
> regions are released to the kernel for general allocation, and so
> exposing them this way only makes sense if you keep them as you do for
> x86.
>
> Could you please try to make this call specific to situations where it
> makes sense? I don't mind allocating a new EFI_xxx flag for preserving
> the boot services regions so we could decide to set it for ARM/arm64
> as well in certain cases in the future.

Ok, I've added a new EFI_BOOT_SERVICES flag for this for v4 of this
patchset, mirroring the existing EFI_RUNTIME_SERVICES flag in naming.

Regards,

Hans