From 3af6d22bb3850ab2bac67287e3a3d3b0e32868e5 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 15 Apr 2024 21:41:07 +0200 Subject: Merging upstream version 6.7. Signed-off-by: Daniel Baumann --- man4/cpuid.4 | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) (limited to 'man4/cpuid.4') diff --git a/man4/cpuid.4 b/man4/cpuid.4 index 3f7d184..e58e29e 100644 --- a/man4/cpuid.4 +++ b/man4/cpuid.4 @@ -3,19 +3,19 @@ .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" -.TH cpuid 4 2022-10-30 "Linux man-pages 6.05.01" +.TH cpuid 4 2024-01-05 "Linux man-pages 6.7" .SH NAME cpuid \- x86 CPUID access device .SH DESCRIPTION CPUID provides an interface for querying information about the x86 CPU. -.PP +.P This device is accessed by .BR lseek (2) or .BR pread (2) to the appropriate CPUID level and reading in chunks of 16 bytes. A larger read size means multiple reads of consecutive levels. -.PP +.P The lower 32 bits of the file position is used as the incoming .IR %eax , and the upper 32 bits of the file position as the incoming @@ -24,7 +24,7 @@ the latter is intended for "counting" .I eax levels like .IR eax=4 . -.PP +.P This driver uses .IR /dev/cpu/CPUNUM/cpuid , where @@ -34,7 +34,7 @@ and on an SMP box will direct the access to CPU .I CPUNUM as listed in .IR /proc/cpuinfo . -.PP +.P This file is protected so that it can be read only by the user .IR root , or members of the group @@ -44,7 +44,7 @@ The CPUID instruction can be directly executed by a program using inline assembler. However this device allows convenient access to all CPUs without changing process affinity. -.PP +.P Most of the information in .I cpuid is reported by the kernel in cooked form either in @@ -53,29 +53,31 @@ or through subdirectories in .IR /sys/devices/system/cpu . Direct CPUID access through this device should only be used in exceptional cases. -.PP +.P The .I cpuid driver is not auto-loaded. On modular kernels you might need to use the following command to load it explicitly before use: -.PP +.P .in +4n .EX $ modprobe cpuid .EE .in -.PP +.P There is no support for CPUID functions that require additional input registers. -.PP -Very old x86 CPUs don't support CPUID. +.P +Early i486 CPUs do not support the CPUID instruction; +.\" arch/x86/kernel/cpuid.c cpuid_open() +opening this device for those CPUs fails with EIO. .SH SEE ALSO .BR cpuid (1) -.PP +.P Intel Corporation, Intel 64 and IA-32 Architectures Software Developer's Manual Volume 2A: Instruction Set Reference, A-M, 3-180 CPUID reference. -.PP +.P Intel Corporation, Intel Processor Identification and the CPUID Instruction, Application note 485. -- cgit v1.2.3