linux-kernel - Re: [PATCH v2 2/3] acpi: allow building without CONFIG_HAS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <e135bc0a-7c06-4ee2-b149-100595a29d7e@app.fastmail.com>
Date: Fri, 11 Oct 2024 11:40:05 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>
Cc: "Arnd Bergmann" <arnd@...nel.org>,
 "Rafael J . Wysocki" <rafael@...nel.org>, "Len Brown" <lenb@...nel.org>,
 "Mario Limonciello" <mario.limonciello@....com>,
 "Jarred White" <jarredwhite@...ux.microsoft.com>,
 "Perry Yuan" <perry.yuan@....com>,
 "Easwar Hariharan" <eahariha@...ux.microsoft.com>,
 linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] acpi: allow building without CONFIG_HAS_IOPORT

On Fri, Oct 11, 2024, at 11:12, Andy Shevchenko wrote:
> On Fri, Oct 11, 2024 at 09:59:46AM +0000, Arnd Bergmann wrote:
>> On Fri, Oct 11, 2024, at 09:53, Andy Shevchenko wrote:
>> > On Fri, Oct 11, 2024 at 06:18:18AM +0000, Arnd Bergmann wrote:
>> >> +	if (!IS_ENABLED(CONFIG_HAS_IOPORT)) {
>> >> +		*value = BIT_MASK(width);
>> >> +		return AE_NOT_IMPLEMENTED;
>> >
>> > Perhaps it has already been discussed, but why do we need to file value with
>> > semi-garbage when we know it's invalid anyway?
>> 
>> It's not strictly necessary, just precaution for possible callers
>> that use the resulting data without checking the error code.
>
> Do you have any examples of that in the kernel?

drivers/acpi/processor_throttling.c:            acpi_os_read_port((acpi_io_address) throttling->status_register.
--
drivers/cpufreq/acpi-cpufreq.c-
drivers/cpufreq/acpi-cpufreq.c: acpi_os_read_port(reg->address, &val, reg->bit_width);

$ git grep ^[^=]*acpi_os_read_port 
drivers/acpi/processor_throttling.c:            acpi_os_read_port(\ (acpi_io_address) throttling->status_register.
drivers/cpufreq/acpi-cpufreq.c: acpi_os_read_port(reg->address, &val, reg->bit_width);

>> The all-ones data is what an x86 PC would see when an I/O
>> port is read that is not connected to any device.
>
> Yes, but it's not what your code does.

My bad, I was confused about what BIT_MASK() does.
I'll change it to "GENMASK(width, 0)", which should
do what I intended.

      Arnd