From: Dave Hansen <dave.hansen@intel.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org, linux-api@vger.kernel.org,
x86@kernel.org, linux-arch@vger.kernel.org,
"H.J. Lu" <hjl.tools@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: x86 CPU features detection for applications (and AMX)
Date: Thu, 8 Jul 2021 07:19:21 -0700 [thread overview]
Message-ID: <b3b104cd-72d9-7f5c-116b-414c6ebf448d@intel.com> (raw)
In-Reply-To: <878s2hz6g3.fsf@oldenburg.str.redhat.com>
On 7/7/21 11:05 PM, Florian Weimer wrote:
>> This looks basically like someone dumped a bunch of CPUID bit values and
>> exposed them to applications without considering whether applications
>> would ever need them. For instance, why would an app ever care about:
>>
>> PKS – Protection keys for supervisor-mode pages.
>>
>> And how could glibc ever give applications accurate information about
>> whether PKS "is supported by the operating system"? It just plain
>> doesn't know, or at least only knows from a really weak ABI like
>> /proc/cpuinfo.
> glibc is expected to mask these bits for CPU_FEATURE_USABLE because they
> have unknown semantics (to glibc).
OK, so if I call CPU_FEATURE_USABLE(PKS) on a system *WITH* PKS
supported in the operating system, I'll get false from an interface that
claims to be:
> This macro returns a nonzero value (true) if the processor has the
> feature name and the feature is supported by the operating system.
The interface just seems buggy by *design*.
next prev parent reply other threads:[~2021-07-08 14:19 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-23 15:04 Florian Weimer
2021-06-23 15:32 ` Dave Hansen
2021-07-08 6:05 ` Florian Weimer
2021-07-08 14:19 ` Dave Hansen [this message]
2021-07-08 14:31 ` Florian Weimer
2021-07-08 14:36 ` Dave Hansen
2021-07-08 14:41 ` Florian Weimer
2021-06-25 23:31 ` Thiago Macieira
[not found] ` <3c5c29e2-1b52-3576-eda2-018fb1e58ff9@metux.net>
2021-06-28 13:20 ` Peter Zijlstra
[not found] ` <534d0171-2cc5-cd0a-904f-cd3c499b55af@metux.net>
2021-06-30 15:36 ` Thiago Macieira
2021-06-28 15:08 ` Thiago Macieira
2021-06-28 15:27 ` Peter Zijlstra
2021-06-28 16:13 ` Thiago Macieira
2021-06-28 17:11 ` Peter Zijlstra
2021-06-28 17:23 ` Thiago Macieira
2021-06-28 19:08 ` Peter Zijlstra
2021-06-28 19:26 ` Thiago Macieira
2021-06-28 17:43 ` Peter Zijlstra
2021-06-28 19:05 ` Thiago Macieira
[not found] ` <e07294c9-b02a-e1c5-3620-7fae7269fdf1@metux.net>
2021-06-30 14:34 ` Florian Weimer
[not found] ` <030f1462-2bf9-39bc-d620-6d9fbe454a27@metux.net>
2021-06-30 15:38 ` Florian Weimer
[not found] ` <4ba30cb7-6854-0691-fad6-4ca9ce674ac2@metux.net>
2021-07-01 8:21 ` Florian Weimer
[not found] ` <034dcf9b-1f8c-23ee-86a6-791122bc0f8c@metux.net>
2021-07-06 12:57 ` Florian Weimer
2021-06-30 15:29 ` Thiago Macieira
2021-07-08 7:08 ` Florian Weimer
2021-07-08 15:13 ` Thiago Macieira
2021-07-08 17:56 ` Mark Brown
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