[MODERATED] Re: [patch V11 14/16] SSB 14

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, May 02, 2018 at 11:51:16PM +0200, speck for Thomas Gleixner wrote:
> Subject: [patch V11 14/16] prctl: Add speculation control prctls
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> Add two new prctls to control aspects of speculation related vulnerabilites
> and their mitigations to provide finer grained control over performance
> impacting mitigations.
> 
> PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature
> which is selected with arg2 of prctl(2). The return value uses bit 0-2 with
> the following meaning:
> 
> Bit  Define           Description
> 0    PR_SPEC_PRCTL    Mitigation can be controlled per task by
>                       PR_SET_SPECULATION_CTRL
> 1    PR_SPEC_ENABLE   The speculation feature is enabled, mitigation is
>                       disabled
> 2    PR_SPEC_DISABLE  The speculation feature is disabled, mitigation is
>                       enabled
> 
> If all bits are 0 the CPU is not affected by the speculation misfeature.
> 
> If PR_SPEC_PRCTL is set, then the per task control of the mitigation is
> available. If not set, prctl(PR_SET_SPECULATION_CTRL) for the speculation
> misfeature will fail.
> 
> PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which
> is selected by arg2 of prctl(2) per task. arg3 is used to hand in the
> control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE.
> 
> The common return values are:
> 
> EINVAL  prctl is not implemented by the architecture or the unused prctl()
>         arguments are not 0
> ENODEV  arg2 is selecting a not supported speculation misfeature
> 
> PR_SET_SPECULATION_CTRL has these additional return values:
> 
> ERANGE  arg3 is incorrect, i.e. it's not either PR_SPEC_ENABLE or PR_SPEC_DISABLE
> ENXIO   prctl control of the selected speculation misfeature is disabled
> 
> The first supported controlable speculation misfeature is
> PR_SPEC_STORE_BYPASS. Add the define so this can be shared between
> architectures.
> 
> TODO: Write a man prctl(2) patch.
> 
> Based on an initial patch from Tim Chen and mostly rewritten.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reviewed-by: Ingo Molnar <mingo@kernel.org>


Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

with the "TODO: Write a man ..." removed from it.