Messages in this thread |  | | Date | Sun, 27 Feb 2022 12:42:03 +0100 | Subject | Re: [PATCH v5 2/3] ACPI: allow longer device IDs | From | Alexander Graf <> |
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On 26.02.22 23:06, Jason A. Donenfeld wrote: > From: Alexander Graf <graf@amazon.com> > > We create a list of ACPI "PNP" IDs which contains _HID, _CID, and CLS > entries of the respective devices. However, we squeeze them into struct > acpi_device_id, which only has 9 bytes space to store the identifier. 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
This is only true for 64bit systems where padding automatically bloated to 9 byte array to 16. I still believe the patch is fine as it is, but there will be minor .rodata overhead on 32bit targets which you may want to quantify in the patch description.
Thanks a lot for sending this out! And let's hope that 16 bytes is enough for everyone.
Alex
> doesn't actually increase vmlinux size, because the ulong in the same > struct caused there to be 7 bytes of padding anyway. > > 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 > > Cc: Ard Biesheuvel <ardb@kernel.org> > Cc: Len Brown <lenb@kernel.org> > Cc: Rafael J. Wysocki <rafael@kernel.org> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Co-authored-by: Jason A. Donenfeld <Jason@zx2c4.com> > Signed-off-by: Alexander Graf <graf@amazon.com> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > Hi Rafael & Len, > > This patchset is directed toward you two specifically. Patches 1/3 and > 3/3 have been through the ringer of review a bit already and do not > specifically require your attention, but in v4 we wound up getting hung > up on an ACPI API limitation. This v5 fixes that limitation with this > 2/3 patch that you see here, with a trivial one line fix, which does > require your attention. > > Patches 1/3 and 3/3 will go through my random.git tree. However, 3/3 > actually depends on this one here, 2/3, in order to compile without > warnings (and be functional at all). Therefore, it would be nice if you > would provide an "Acked-by" on it and permit me to /also/ take it > through my random.git tree (if it looks like a correct patch to you, of > course). This would make the merge logistics a lot easier. Plus it's a > small +1/-1 line change. > > Please have a look and let me know what you think. > > Thanks, > Jason > > include/linux/mod_devicetable.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > 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]; > -- > 2.35.1 >
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