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bh=zF19XFFiqPbLLTSJfpDVbR2CVLpYKiYAcawYZXkE6BY=; b=ek9+Spjyg+ItTrpdrr4zw6x/YyHiJ36bDHL03LrnPGMvpbteOcRMvfKo vmmM1oFL9GWnCugpmVa5rKgV37WunWJZDKPHykXPZv9XzqYr/Rjj3dVoE A4Kv9E/mwfZ7V0nR3Y2HcU8WgqkfdqoDoCguhHs1XGY+jkZfQ77/Bx+jq FQ1Dpr/UC/NcV9VwG8ER+OgwNaG27We+k0PQVgpFJFKlPxI35qTPrqVHR huZTfJW0SXiK4dWZlz68QouOGEyVPPJmUUxZMGlyoGL434J3uCNL4M7nN OMGasIkjrpw23BeliYe8LqXndtAaCJf7Z0JLFYovNlBwNi67nZ+hrxmSn A==; X-IronPort-AV: E=McAfee;i="6600,9927,10961"; a="1150236" X-IronPort-AV: E=Sophos;i="6.05,211,1701158400"; d="scan'208";a="1150236" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Jan 2024 09:20:51 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,211,1701158400"; d="scan'208";a="1262897" Received: from b4969161e530.jf.intel.com ([10.165.56.46]) by orviesa005.jf.intel.com with ESMTP; 22 Jan 2024 09:20:50 -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 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 Subject: [PATCH v7 14/15] Docs/x86/sgx: Add description for cgroup support Date: Mon, 22 Jan 2024 09:20:47 -0800 Message-Id: <20240122172048.11953-15-haitao.huang@linux.intel.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20240122172048.11953-1-haitao.huang@linux.intel.com> References: <20240122172048.11953-1-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: 1788820471605622128 X-GMAIL-MSGID: 1788820471605622128 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 --- 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 | 74 ++++++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) diff --git a/Documentation/arch/x86/sgx.rst b/Documentation/arch/x86/sgx.rst index d90796adc2ec..dfc8fac13ab2 100644 --- a/Documentation/arch/x86/sgx.rst +++ b/Documentation/arch/x86/sgx.rst @@ -300,3 +300,77 @@ 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.