linux-kernel - Re: [tip:efi/core] efibc: Add EFI Bootloader Control module

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Date:	Sat, 30 Apr 2016 10:33:32 +0200
From:	jeremy.compostella@...el.com (Compostella, Jeremy)
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Matt Fleming <matt@...eblueprint.co.uk>,
	<stefan.stanacar@...el.com>, <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
	<hpa@...or.com>, <bp@...en8.de>, <ard.biesheuvel@...aro.org>,
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:efi/core] efibc: Add EFI Bootloader Control module

Ingo Molnar <mingo@...nel.org> writes:

> * Compostella, Jeremy <jeremy.compostella@...el.com> wrote:
>
>> -static void efibc_set_variable(const char *name, const char *value)
>> +static int efibc_set_variable(const char *name, const char *value)
>>  {
>>  	int ret;
>>  	efi_guid_t guid = LINUX_EFI_LOADER_ENTRY_GUID;
>> -	struct efivar_entry entry;
>> +	struct efivar_entry *entry;
>>  	size_t size = (strlen(value) + 1) * sizeof(efi_char16_t);
>>  
>> -	if (size > sizeof(entry.var.Data))
>> +	if (size > sizeof(entry->var.Data)) {
>>  		pr_err("value is too large");
>> +		return -1;
>> +	}
>>  
>> -	efibc_str_to_str16(name, entry.var.VariableName);
>> -	efibc_str_to_str16(value, (efi_char16_t *)entry.var.Data);
>> -	memcpy(&entry.var.VendorGuid, &guid, sizeof(guid));
>> +	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
>> +	if (!entry) {
>> +		pr_err("failed to allocate efivar entry");
>> +		return -1;
>> +	}
>>  
>> -	ret = efivar_entry_set(&entry,
>> +	efibc_str_to_str16(name, entry->var.VariableName);
>> +	efibc_str_to_str16(value, (efi_char16_t *)entry->var.Data);
>> +	memcpy(&entry->var.VendorGuid, &guid, sizeof(guid));
>> +
>> +	ret = efivar_entry_set(entry,
>>  			       EFI_VARIABLE_NON_VOLATILE
>>  			       | EFI_VARIABLE_BOOTSERVICE_ACCESS
>>  			       | EFI_VARIABLE_RUNTIME_ACCESS,
>> -			       size, entry.var.Data, NULL);
>> +			       size, entry->var.Data, NULL);
>>  	if (ret)
>>  		pr_err("failed to set %s EFI variable: 0x%x\n",
>>  		       name, ret);
>> +
>> +	kfree(entry);
>> +	return ret;
>>  }
>>  
>>  static int efibc_reboot_notifier_call(struct notifier_block *notifier,
>>  				      unsigned long event, void *data)
>>  {
>>  	const char *reason = "shutdown";
>> +	int ret;
>>  
>>  	if (event == SYS_RESTART)
>>  		reason = "reboot";
>>  
>> -	efibc_set_variable("LoaderEntryRebootReason", reason);
>> -
>> -	if (!data)
>> -		return NOTIFY_DONE;
>> +	ret = efibc_set_variable("LoaderEntryRebootReason", reason);
>> +	if (ret || !data)
>> + 		return NOTIFY_DONE;
>>  
>>  	efibc_set_variable("LoaderEntryOneShot", (char *)data);
>
> Hm, can reboot notifiers do non-atomic allocations?
The reboot notifier chain is a blocking notifier chain. AFAIK, it
allows non-atomic allocation, right ?

> Why is efivar_entry so huge?
efivar_entry structure include two "big" arrays of 1024 bytes each for
the EFI variable name and data.

Thanks,

Jérémy
-- 
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