From mboxrd@z Thu Jan 1 00:00:00 1970 From: Haitao Huang Subject: [PATCH v4 17/18] Docs/x86/sgx: Add description for cgroup support Date: Tue, 12 Sep 2023 21:06:34 -0700 Message-ID: <20230913040635.28815-18-haitao.huang@linux.intel.com> References: <20230913040635.28815-1-haitao.huang@linux.intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1694578140; x=1726114140; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=hEu3sY0L0Zm8yUMNRt51Y+KGZj58gXXJpRMwbPXfe14=; b=gaqSnY94y3UF2pguqjfrkbYW5gdGM8xzqQbZFSOGj65LIVAJpmBpZgxA u06VPICdNuNON9OBvhyD32NIOePuqpf1TVpvHJ6PfAqdFt1J9G8Zvt/H1 QMGBDU6D5MXdsq6tBfpYrdk2ySg7KNGqVm9bk4UO0aTvEU8XYC1El9P8H FCkyPaRlwWjCZtF7gB1QvMqzT7PlDJrtSbRVe0zpYeqlxl+6NxvcWSZ+R IyDlTLMd/yhpn5LTolwJTuc6+BX+WkRvSDy8rgnO3i1Thze04pWDU7mNJ jGx9Q6BJeGxuHUfSvtc4yAZ3vu6VUtRMMTsRBIpp2lNJlBZd66RGHviVL A==; In-Reply-To: <20230913040635.28815-1-haitao.huang-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" To: jarkko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, dave.hansen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sgx-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org, mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, bp-Gina5bIWoIWzQB+pC5nmwQ@public.gmane.org, hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org, sohil.mehta-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org Cc: zhiquan1.li-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, kristen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, seanjc-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, zhanb-0li6OtcxBFHby3iVrkZq2A@public.gmane.org, anakrish-0li6OtcxBFHby3iVrkZq2A@public.gmane.org, mikko.ylinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, yangjie-0li6OtcxBFHby3iVrkZq2A@public.gmane.org From: Kristen Carlson Accardi Add initial documentation of how to regulate the distribution of SGX Enclave Page Cache (EPC) memory via the Miscellaneous cgroup controller. Signed-off-by: Sean Christopherson Signed-off-by: Kristen Carlson Accardi Signed-off-by: Haitao Huang Cc: Sean Christopherson Reviewed-by: Bagas Sanjaya --- V4: - Fix indentation (Randy) - Change misc.events file to be read-only - Fix a typo for 'subsystem' - Add behavior when VMM overcommit EPC with a cgroup (Mikko) --- Documentation/arch/x86/sgx.rst | 82 ++++++++++++++++++++++++++++++++++ 1 file changed, 82 insertions(+) diff --git a/Documentation/arch/x86/sgx.rst b/Documentation/arch/x86/sgx.rst index d90796adc2ec..65c211bd5342 100644 --- a/Documentation/arch/x86/sgx.rst +++ b/Documentation/arch/x86/sgx.rst @@ -300,3 +300,85 @@ to expected failures and handle them as follows: first call. It indicates a bug in the kernel or the userspace client if any of the second round of ``SGX_IOC_VEPC_REMOVE_ALL`` calls has a return code other than 0. + + +Cgroup Support +============== + +The "sgx_epc" resource within the Miscellaneous cgroup controller regulates +distribution of SGX EPC memory, which is a subset of system RAM that +is used to provide SGX-enabled applications with protected memory, +and is otherwise inaccessible, i.e. shows up as reserved in +/proc/iomem and cannot be read/written outside of an SGX enclave. + +Although current systems implement EPC by stealing memory from RAM, +for all intents and purposes the EPC is independent from normal system +memory, e.g. must be reserved at boot from RAM and cannot be converted +between EPC and normal memory while the system is running. The EPC is +managed by the SGX subsystem and is not accounted by the memory +controller. Note that this is true only for EPC memory itself, i.e. +normal memory allocations related to SGX and EPC memory, e.g. the +backing memory for evicted EPC pages, are accounted, limited and +protected by the memory controller. + +Much like normal system memory, EPC memory can be overcommitted via +virtual memory techniques and pages can be swapped out of the EPC +to their backing store (normal system memory allocated via shmem). +The SGX EPC subsystem is analogous to the memory subsystem, and +it implements limit and protection models for EPC memory. + +SGX EPC Interface Files +----------------------- + +For a generic description of the Miscellaneous controller interface +files, please see Documentation/admin-guide/cgroup-v2.rst + +All SGX EPC memory amounts are in bytes unless explicitly stated +otherwise. If a value which is not PAGE_SIZE aligned is written, +the actual value used by the controller will be rounded down to +the closest PAGE_SIZE multiple. + + misc.capacity + A read-only flat-keyed file shown only in the root cgroup. + The sgx_epc resource will show the total amount of EPC + memory available on the platform. + + misc.current + A read-only flat-keyed file shown in the non-root cgroups. + The sgx_epc resource will show the current active EPC memory + usage of the cgroup and its descendants. EPC pages that are + swapped out to backing RAM are not included in the current count. + + misc.max + A read-write single value file which exists on non-root + cgroups. The sgx_epc resource will show the EPC usage + hard limit. The default is "max". + + If a cgroup's EPC usage reaches this limit, EPC allocations, + e.g. for page fault handling, will be blocked until EPC can + be reclaimed from the cgroup. If EPC cannot be reclaimed in + a timely manner, reclaim will be forced, e.g. by ignoring LRU. + + The EPC pages allocated for KVM guests by the virtual EPC driver + are not reclaimable by the host kernel SGX reclaimers. If a VMM + tries to start a VM within a cgroup whose EPC usage reaches this + limit, the virtual EPC driver will stop allocating more EPC for the + VM, and return SIGBUS to the VMM which would abort the VM launch. + + misc.events + A read-only flat-keyed file which exists on non-root cgroups. + A value change in this file generates a file modified event. + + max + The number of times the cgroup has triggered a reclaim + due to its EPC usage approaching (or exceeding) its max + EPC boundary. + +Migration +--------- + +Once an EPC page is charged to a cgroup (during allocation), it +remains charged to the original cgroup until the page is released +or reclaimed. Migrating a process to a different cgroup doesn't +move the EPC charges that it incurred while in the previous cgroup +to its new cgroup. -- 2.25.1