Re: [PATCH v4 6/8] efi: load SSTDs from EFI variables

[Octavian Purdila]

On Thu, Jun 23, 2016 at 4:22 PM, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote:

> On Fri, 17 Jun, at 02:52:14PM, Octavian Purdila wrote:
>> This patch allows SSDTs to be loaded from EFI variables. It works by
>> specifying the EFI variable name containing the SSDT to be loaded. All
>> variables with the same name (regardless of the vendor GUID) will be
>> loaded.
>>
>> Note that we can't use acpi_install_table and we must rely on the
>> dynamic ACPI table loading and bus re-scanning mechanisms. That is
>> because I2C/SPI controllers are initialized earlier then the EFI
>> subsystems and all I2C/SPI ACPI devices are enumerated when the
>> I2C/SPI controllers are initialized.
>>
>> Signed-off-by: Octavian Purdila <octavian.purdila@xxxxxxxxx>
>> ---
>>  Documentation/acpi/ssdt-overlays.txt |  67 ++++++++++++++++++++++
>>  Documentation/kernel-parameters.txt  |   7 +++
>>  drivers/firmware/efi/efi.c           | 106 +++++++++++++++++++++++++++++++++++
>>  3 files changed, 180 insertions(+)
>
> [...]
>
>> @@ -195,6 +197,107 @@ static void generic_ops_unregister(void)
>>       efivars_unregister(&generic_efivars);
>>  }
>>
>> +#if IS_ENABLED(CONFIG_ACPI)
>> +#define EFIVAR_SSDT_NAME_MAX 16
>> +static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX];
>> +static int __init efivar_ssdt_setup(char *str)
>> +{
>> +     if (strlen(str) < sizeof(efivar_ssdt))
>> +             memcpy(efivar_ssdt, str, strlen(str));
>> +     else
>> +             pr_warn("efivar_ssdt: name too long: %s\n", str);
>> +     return 0;
>> +}
>> +__setup("efivar_ssdt=", efivar_ssdt_setup);
>> +
>> +static LIST_HEAD(efivar_ssdts);
>> +
>> +static inline void pr_efivar_name(efi_char16_t *name16)
>> +{
>> +     char name[EFIVAR_SSDT_NAME_MAX];
>> +     int i;
>> +
>> +     for (i = 0; i < EFIVAR_SSDT_NAME_MAX - 1; i++)
>> +             name[i] = name16[i] & 0xFF;
>> +     name[i] = 0;
>> +     pr_cont("%s", name);
>> +}
>
> Please use the various ucs2_* functions we already have in lib/.
>

Okay, after reading the archives regarding UTF8, ucs2, etc. it looks
like the best thing to do in kernel is to avoid interpreting them. So
I'll just print the kernel command line parameter and use ucs2_as_utf8
and memcmp to check if the variable name matches the kernel command
line.

>> +static __init int efivar_acpi_iter(efi_char16_t *name, efi_guid_t vendor,
>> +                                unsigned long name_size, void *data)
>> +{
>> +     int i;
>> +     int str_len = name_size / sizeof(efi_char16_t);
>> +     struct efivar_entry *entry;
>> +
>> +     if (str_len != strlen(efivar_ssdt) + 1)
>> +             return 0;
>> +
>> +     for (i = 0; i < str_len; i++)
>> +             if ((name[i] & 0xFF) != efivar_ssdt[i])
>> +                     return 0;
>> +
>> +     entry = kzalloc(sizeof(*entry), GFP_KERNEL);
>> +     if (!entry)
>> +             return -ENOMEM;
>> +
>> +     memcpy(entry->var.VariableName, name, name_size);
>> +     memcpy(&entry->var.VendorGuid, &vendor, sizeof(efi_guid_t));
>> +
>> +     efivar_entry_add(entry, &efivar_ssdts);
>> +
>> +     return 0;
>> +}
>> +
>> +static __init int efivar_ssdt_load(void)
>> +{
>> +     struct efivar_entry *i;
>> +     int err;
>> +
>> +     err = efivar_init(efivar_acpi_iter, NULL, true, &efivar_ssdts);
>> +     if (err) {
>> +             pr_err("%s: efivar_init failed: %d\n", __func__, err);
>> +             return err;
>> +     }
>> +
>> +     list_for_each_entry(i, &efivar_ssdts, list) {
>> +             void *data;
>> +             unsigned long size;
>> +
>> +             pr_info("loading SSDT from EFI variable ");
>> +             pr_efivar_name(i->var.VariableName); pr_cont("\n");
>> +
>> +             err = efivar_entry_size(i, &size);
>> +             if (err) {
>> +                     pr_err("failed to get size\n");
>> +                     continue;
>> +             }
>> +
>> +             data = kmalloc(size, GFP_KERNEL);
>> +             if (!data)
>> +                     continue;
>> +
>> +             err = efivar_entry_get(i, NULL, &size, data);
>> +             if (err) {
>> +                     pr_err("failed to get data\n");
>> +                     kfree(data);
>> +                     continue;
>> +             }
>> +
>> +             err = acpi_load_table(data);
>> +             if (err) {
>> +                     pr_err("failed to load table: %d\n", err);
>> +                     kfree(data);
>> +                     continue;
>> +             }
>> +     }
>> +
>
> Since 'efivar_ssdts' isn't exported to userspace and is never
> traversed again after its built in efivar_acpi_iter(), can't you just
> fold the code from the above list_for_each_entry() loop into
> efivar_acpi_iter()?
>
> You should be able to call efivar_entry_get() without 'entry' actually
> being on any list since the list is only used for duplicate variable
> detection in this case.

Since commit 1cfd63166 (efi: Merge boolean flag arguments) it is a bit
hairy to do this. We need to call efivar_init() with duplicates set to
false to allow passing a  NULL list but in that case the __efivars
lock is not release when calling the iterator function which means
that calls like efivar_entry_get from within the iterator function
will deadlock.

What seems to work is to call efivar_init() with duplicates set and
pass a temporary empty list. How does that sound?