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    Subject[tip:x86/cache] x86/intel_rdt: Utilities to restrict/restore access to specific files
    Commit-ID:  2a5d76a4fc6469ea9dd6f02fcd4dad3a129bc1c0
    Gitweb: https://git.kernel.org/tip/2a5d76a4fc6469ea9dd6f02fcd4dad3a129bc1c0
    Author: Reinette Chatre <reinette.chatre@intel.com>
    AuthorDate: Fri, 22 Jun 2018 15:42:13 -0700
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Sat, 23 Jun 2018 13:03:46 +0200

    x86/intel_rdt: Utilities to restrict/restore access to specific files

    In support of Cache Pseudo-Locking we need to restrict access to specific
    resctrl files to protect the state of a resource group used for
    pseudo-locking from being changed in unsupported ways.

    Introduce two utilities that can be used to either restrict or restore the
    access to all files irrelevant to cache pseudo-locking when pseudo-locking
    in progress for the resource group.

    At this time introduce a new source file, intel_rdt_pseudo_lock.c, that
    will contain most of the code related to cache pseudo-locking.

    Temporarily mark these new functions as unused to silence compile warnings
    until they are used.

    Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: fenghua.yu@intel.com
    Cc: tony.luck@intel.com
    Cc: vikas.shivappa@linux.intel.com
    Cc: gavin.hindman@intel.com
    Cc: jithu.joseph@intel.com
    Cc: dave.hansen@intel.com
    Cc: hpa@zytor.com
    Link: https://lkml.kernel.org/r/ab6319d1244366be3f9b7f9fba1c3da4810a274b.1529706536.git.reinette.chatre@intel.com

    ---
    arch/x86/kernel/cpu/Makefile | 3 +-
    arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c | 113 ++++++++++++++++++++++++++++
    2 files changed, 115 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
    index 7a40196967cb..c4e02555563a 100644
    --- a/arch/x86/kernel/cpu/Makefile
    +++ b/arch/x86/kernel/cpu/Makefile
    @@ -35,7 +35,8 @@ obj-$(CONFIG_CPU_SUP_CENTAUR) += centaur.o
    obj-$(CONFIG_CPU_SUP_TRANSMETA_32) += transmeta.o
    obj-$(CONFIG_CPU_SUP_UMC_32) += umc.o

    -obj-$(CONFIG_INTEL_RDT) += intel_rdt.o intel_rdt_rdtgroup.o intel_rdt_monitor.o intel_rdt_ctrlmondata.o
    +obj-$(CONFIG_INTEL_RDT) += intel_rdt.o intel_rdt_rdtgroup.o intel_rdt_monitor.o
    +obj-$(CONFIG_INTEL_RDT) += intel_rdt_ctrlmondata.o intel_rdt_pseudo_lock.o

    obj-$(CONFIG_X86_MCE) += mcheck/
    obj-$(CONFIG_MTRR) += mtrr/
    diff --git a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
    new file mode 100644
    index 000000000000..dc79b3090ac5
    --- /dev/null
    +++ b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
    @@ -0,0 +1,113 @@
    +// SPDX-License-Identifier: GPL-2.0
    +/*
    + * Resource Director Technology (RDT)
    + *
    + * Pseudo-locking support built on top of Cache Allocation Technology (CAT)
    + *
    + * Copyright (C) 2018 Intel Corporation
    + *
    + * Author: Reinette Chatre <reinette.chatre@intel.com>
    + */
    +
    +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    +
    +#include "intel_rdt.h"
    +
    +/**
    + * rdtgroup_locksetup_user_restrict - Restrict user access to group
    + * @rdtgrp: resource group needing access restricted
    + *
    + * A resource group used for cache pseudo-locking cannot have cpus or tasks
    + * assigned to it. This is communicated to the user by restricting access
    + * to all the files that can be used to make such changes.
    + *
    + * Permissions restored with rdtgroup_locksetup_user_restore()
    + *
    + * Return: 0 on success, <0 on failure. If a failure occurs during the
    + * restriction of access an attempt will be made to restore permissions but
    + * the state of the mode of these files will be uncertain when a failure
    + * occurs.
    + */
    +static int __attribute__ ((unused))
    +rdtgroup_locksetup_user_restrict(struct rdtgroup *rdtgrp)
    +{
    + int ret;
    +
    + ret = rdtgroup_kn_mode_restrict(rdtgrp, "tasks");
    + if (ret)
    + return ret;
    +
    + ret = rdtgroup_kn_mode_restrict(rdtgrp, "cpus");
    + if (ret)
    + goto err_tasks;
    +
    + ret = rdtgroup_kn_mode_restrict(rdtgrp, "cpus_list");
    + if (ret)
    + goto err_cpus;
    +
    + if (rdt_mon_capable) {
    + ret = rdtgroup_kn_mode_restrict(rdtgrp, "mon_groups");
    + if (ret)
    + goto err_cpus_list;
    + }
    +
    + ret = 0;
    + goto out;
    +
    +err_cpus_list:
    + rdtgroup_kn_mode_restore(rdtgrp, "cpus_list");
    +err_cpus:
    + rdtgroup_kn_mode_restore(rdtgrp, "cpus");
    +err_tasks:
    + rdtgroup_kn_mode_restore(rdtgrp, "tasks");
    +out:
    + return ret;
    +}
    +
    +/**
    + * rdtgroup_locksetup_user_restore - Restore user access to group
    + * @rdtgrp: resource group needing access restored
    + *
    + * Restore all file access previously removed using
    + * rdtgroup_locksetup_user_restrict()
    + *
    + * Return: 0 on success, <0 on failure. If a failure occurs during the
    + * restoration of access an attempt will be made to restrict permissions
    + * again but the state of the mode of these files will be uncertain when
    + * a failure occurs.
    + */
    +static int __attribute__ ((unused))
    +rdtgroup_locksetup_user_restore(struct rdtgroup *rdtgrp)
    +{
    + int ret;
    +
    + ret = rdtgroup_kn_mode_restore(rdtgrp, "tasks");
    + if (ret)
    + return ret;
    +
    + ret = rdtgroup_kn_mode_restore(rdtgrp, "cpus");
    + if (ret)
    + goto err_tasks;
    +
    + ret = rdtgroup_kn_mode_restore(rdtgrp, "cpus_list");
    + if (ret)
    + goto err_cpus;
    +
    + if (rdt_mon_capable) {
    + ret = rdtgroup_kn_mode_restore(rdtgrp, "mon_groups");
    + if (ret)
    + goto err_cpus_list;
    + }
    +
    + ret = 0;
    + goto out;
    +
    +err_cpus_list:
    + rdtgroup_kn_mode_restrict(rdtgrp, "cpus_list");
    +err_cpus:
    + rdtgroup_kn_mode_restrict(rdtgrp, "cpus");
    +err_tasks:
    + rdtgroup_kn_mode_restrict(rdtgrp, "tasks");
    +out:
    + return ret;
    +}
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