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authorAlexander Graf <graf@amazon.com>2022-02-25 18:55:52 +0300
committerJason A. Donenfeld <Jason@zx2c4.com>2022-03-13 04:00:56 +0300
commitd273845ecb0e0626842782a4497f0c5876139ec3 (patch)
treee0a1884372904f55b9aaa9e4f775f909887da8f2
parentae099e8e98fb01395228628be5a4661e3bd86fe4 (diff)
downloadlinux-d273845ecb0e0626842782a4497f0c5876139ec3.tar.xz
ACPI: allow longer device IDs
We create a list of ACPI "PNP" IDs which contains _HID, _CID, and CLS entries of the respective devices. However, when making structs for matching, we squeeze those IDs into acpi_device_id, which only has 9 bytes space to store the identifier. The subsystem actually captures the full length of the IDs, and the modalias has the full length, but this struct we use for matching is limited. It originally had 16 bytes, but was changed to only have 9 in 6543becf26ff ("mod/file2alias: make modalias generation safe for cross compiling"), presumably on the theory that it would match the ACPI spec so it didn't matter. Unfortunately, while most people adhere to the ACPI specs, Microsoft decided that its VM Generation Counter device [1] should only be identifiable by _CID with a value of "VM_Gen_Counter", which is longer than 9 characters. To allow device drivers to match identifiers that exceed the 9 byte limit, this simply ups the length to 16, just like it was before the aforementioned commit. Empirical testing indicates that this doesn't actually increase vmlinux size on 64-bit, because the ulong in the same struct caused there to be 7 bytes of padding anyway, and when doing a s/M/Y/g i386_defconfig build, the bzImage only increased by 0.0055%, so negligible. This patch is a prerequisite to add support for VMGenID in Linux, the subsequent patch in this series. It has been confirmed to also work on the udev/modalias side in userspace. [1] https://download.microsoft.com/download/3/1/C/31CFC307-98CA-4CA5-914C-D9772691E214/VirtualMachineGenerationID.docx Signed-off-by: Alexander Graf <graf@amazon.com> Co-developed-by: Jason A. Donenfeld <Jason@zx2c4.com> [Jason: reworked commit message a bit, went with len=16 approach.] Cc: Mika Westerberg <mika.westerberg@linux.intel.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Len Brown <lenb@kernel.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Hans de Goede <hdegoede@redhat.com> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
-rw-r--r--include/linux/mod_devicetable.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 4bb71979a8fd..5da5d990ff58 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -211,7 +211,7 @@ struct css_device_id {
kernel_ulong_t driver_data;
};
-#define ACPI_ID_LEN 9
+#define ACPI_ID_LEN 16
struct acpi_device_id {
__u8 id[ACPI_ID_LEN];