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bh=9w5lQ2pOZdanN4uPSlw3FqAR9K1n/EpTv9COUE47BCo=; b=RE/D+ThqsP7PQVF4DjgR7PuKRIC27Nnd9LfbNMA6X8gu88J/FlZ8mKuG 9QEPyR/zpe4uxcm27zUtcaKA5sUhrfx6BIDiktAR0l5fxnLgnhhN+VZQI 9HAYiV+53oe+IsVhpgQTcglv2RAl42kRBh8LXAeWsor8nk8xdk4hqGe7V 9wGKu4DxtwJ/IhIRWuS3zWhg9qYoSgeVZjKEGRBRF21fNJ13Of7m4I+XK oYCPB+8VDNtU37v9uFm+LoFdcstIorm866QLs3QdOp+KmAtyDsWzWb8kZ Mmjf8zgzmOsgZuuBkl/iRg9YMRaAMRuZ7isMhK0nJeK+SXl1EWsUml8VZ g==; X-IronPort-AV: E=McAfee;i="6600,9927,10975"; a="11960477" X-IronPort-AV: E=Sophos;i="6.05,245,1701158400"; d="scan'208";a="11960477" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2024 13:06:43 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,245,1701158400"; d="scan'208";a="38245654" Received: from b4969161e530.jf.intel.com ([10.165.56.46]) by orviesa001.jf.intel.com with ESMTP; 05 Feb 2024 13:06:43 -0800 From: Haitao Huang To: jarkko@kernel.org, dave.hansen@linux.intel.com, tj@kernel.org, mkoutny@suse.com, linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org, x86@kernel.org, cgroups@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, sohil.mehta@intel.com, tim.c.chen@linux.intel.com Cc: zhiquan1.li@intel.com, kristen@linux.intel.com, seanjc@google.com, zhanb@microsoft.com, anakrish@microsoft.com, mikko.ylinen@linux.intel.com, yangjie@microsoft.com, chrisyan@microsoft.com Subject: [PATCH v9 14/15] Docs/x86/sgx: Add description for cgroup support Date: Mon, 5 Feb 2024 13:06:37 -0800 Message-Id: <20240205210638.157741-15-haitao.huang@linux.intel.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20240205210638.157741-1-haitao.huang@linux.intel.com> References: <20240205210638.157741-1-haitao.huang@linux.intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1790098123980739372 X-GMAIL-MSGID: 1790098123980739372 From: Sean Christopherson 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 Co-developed-by: Kristen Carlson Accardi Signed-off-by: Kristen Carlson Accardi Co-developed-by: Haitao Huang Signed-off-by: Haitao Huang Cc: Sean Christopherson --- V8: - Limit text width to 80 characters to be consistent. V6: - Remove mentioning of VMM specific behavior on handling SIGBUS - Remove statement of forced reclamation, add statement to specify ENOMEM returned when no reclamation possible. - Added statements on the non-preemptive nature for the max limit - Dropped Reviewed-by tag because of changes 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 | 83 ++++++++++++++++++++++++++++++++++ 1 file changed, 83 insertions(+) diff --git a/Documentation/arch/x86/sgx.rst b/Documentation/arch/x86/sgx.rst index d90796adc2ec..c537e6a9aa65 100644 --- a/Documentation/arch/x86/sgx.rst +++ b/Documentation/arch/x86/sgx.rst @@ -300,3 +300,86 @@ 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 there are no pages left that are reclaimable within the same + group, the kernel returns ENOMEM. + + The EPC pages allocated for a guest VM by the virtual EPC driver are not + reclaimable by the host kernel. In case the guest cgroup's limit is + reached and no reclaimable pages left in the same cgroup, the virtual + EPC driver returns SIGBUS to the user space process to indicate failure + on new EPC allocation requests. + + The misc.max limit is non-preemptive. If a user writes a limit lower + than the current usage to this file, the cgroup will not preemptively + deallocate pages currently in use, and will only start blocking the next + allocation and reclaiming EPC at that time. + + 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.