Re: [PATCH] arch_prctl.2: Add ARCH_SET_CPUID subcommand

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

Hello Keno,

On 3/16/20 4:21 AM, Keno Fischer wrote:
> This subcommand was added a few years ago to support cpuid emulation
> on x86 targets, but no changes to the man page appear to have been
> made at the time. This commit adds a description for it and the
> corresponding getter.
> 
> Signed-off-by: Keno Fischer <keno@juliacomputing.com>

Thanks. Patch applied.

Cheers,

Michael


> ---
>  man2/arch_prctl.2 | 43 ++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/man2/arch_prctl.2 b/man2/arch_prctl.2
> index c49f4e0..e40d6bb 100644
> --- a/man2/arch_prctl.2
> +++ b/man2/arch_prctl.2
> @@ -48,7 +48,44 @@ for the "set" operations, or as an
>  .IR "unsigned long\ *" ,
>  for the "get" operations.
>  .PP
> -Subfunctions for x86-64 are:
> +Subfunctions for both x86 and x86-64 are:
> +.TP
> +.BR ARCH_SET_CPUID " (since Linux 4.12)"
> +Enable (
> +.I addr != 0
> +) or disable (
> +.I addr == 0
> +) the
> +.I cpuid
> +instruction for the current thread. The instruction
> +is enabled by default. If disabled,
> +any execution of a
> +.I cpuid
> +instruction will instead generate a
> +.B SIGSEGV
> +signal. This feature can be used to emulate
> +.I cpuid
> +results that differ from what the underlying
> +hardware would have produced (e.g. in a paravirtualization setting).
> +This setting is preserved across
> +.BR fork (2)
> +and
> +.BR clone (2)
> +but reset to default (i.e.
> +.I cpuid
> +enabled) on
> +.BR execve (2)
> +.
> +.TP
> +.BR ARCH_GET_CPUID " (since Linux 4.12)"
> +Return the setting of the flag manipulated by
> +.B ARCH_SET_CPUID
> +as the result of the system call (1 for enabled, 0 for disabled).
> +.I addr
> +is ignored.
> +
> +.TP
> +Subfunctions for x86-64 only are:
>  .TP
>  .B ARCH_SET_FS
>  Set the 64-bit base for the
> @@ -96,6 +133,10 @@ is not a valid subcommand.
>  .B EPERM
>  .I addr
>  is outside the process address space.
> +.TP
> +.B ENODEV
> +.B ARCH_SET_CPUID
> +was requested, but the underlying hardware does not support CPUID faulting.
>  .\" .SH AUTHOR
>  .\" Man page written by Andi Kleen.
>  .SH CONFORMING TO
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/