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SubjectRe: [PATCH 1/2] efi: Export boot-services code and data as debugfs-blobs
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Hi,

On 03/31/2018 04:10 PM, Greg Kroah-Hartman wrote:
> On Sat, Mar 31, 2018 at 02:19:43PM +0200, Hans de Goede 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@redhat.com>
>> ---
>> arch/x86/platform/efi/quirks.c | 4 +++
>> drivers/firmware/efi/efi.c | 57 ++++++++++++++++++++++++++++++++++
>> 2 files changed, 61 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..fddc5f706fd2 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 +317,59 @@ 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
>> +
>> +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)) {
>> + pr_warn("Could not create efi debugfs entry\n");
>> + return;
>> + }
>
> {sigh}
>
> No, don't warn, or complain, or do anything else if a debugfs call
> fails. Just keep on moving, you can always use the return value
> properly in any future call if you need it, and no code flow should ever
> care if a debugfs call succeeded or failed.

Ok.

>> /*
>> * 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 +414,9 @@ static int __init efisubsys_init(void)
>> goto err_remove_group;
>> }
>>
>> + if (efi_enabled(EFI_DBG))
>> + efi_debugfs_init();
>
> You never remove the directory?

Correct, this is happening from a subsys_initcall as such there is no
efi_cleanup() counterpart.

Note the "if (efi_enabled(EFI_DBG))" check checks for efi=debug on the
kernel cmdline, so this only happens if the user asked for it.

Regards,

Hans

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