Re: [PATCH v2 2/6] prctl.2: Add PR_SPEC_INDIRECT_BRANCH for SPECULATION_CTRL prctls

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Hi Dave,

On Wed, 27 May 2020 at 23:18, Dave Martin <Dave.Martin@xxxxxxx> wrote:
>
> Add the PR_SPEC_INDIRECT_BRANCH "misfeature" added in Linux 4.20
> for PR_SET_SPECULATION_CTRL and PR_GET_SPECULATION_CTRL.
>
> Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

I had also applied this patch from the email you sent earlier. I've
pushed those changes to master now.

Thanks,

Michael

> ---
>  man2/prctl.2 | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/man2/prctl.2 b/man2/prctl.2
> index dc99218..b6fb51c 100644
> --- a/man2/prctl.2
> +++ b/man2/prctl.2
> @@ -1213,11 +1213,20 @@ arguments must be specified as 0; otherwise the call fails with the error
>  .\" commit 356e4bfff2c5489e016fdb925adbf12a1e3950ee
>  Sets the state of the speculation misfeature specified in
>  .IR arg2 .
> -Currently, the only permitted value for this argument is
> +Currently, this argument must be one of:
> +.RS
> +.TP
>  .B PR_SPEC_STORE_BYPASS
> -(otherwise the call fails with the error
> +speculative store bypass control, or
> +.\" commit 9137bb27e60e554dab694eafa4cca241fa3a694f
> +.TP
> +.BR PR_SPEC_INDIRECT_BRANCH " (since Linux 4.20)"
> +indirect branch speculation control.
> +.RE
> +.IP
> +(Otherwise the call fails with the error
>  .BR ENODEV ).
> -This setting is a per-thread attribute.
> +These settings are per-thread attributes.
>  The
>  .IR arg3
>  argument is used to hand in the control value,
> @@ -1235,13 +1244,16 @@ Same as
>  .BR PR_SPEC_DISABLE ,
>  but cannot be undone.
>  A subsequent
> -.B
> -prctl(..., PR_SPEC_ENABLE)
> +.BR prctl (\c
> +.IR arg2 ,
> +.BR PR_SPEC_ENABLE )
> +with the same value for
> +.I arg2
>  will fail with the error
>  .BR EPERM .
>  .RE
>  .IP
> -Any other value in
> +Any unsupported value in
>  .IR arg3
>  will result in the call failing with the error
>  .BR ERANGE .
> --
> 2.1.4
>


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



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