From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751542AbeBXWR2 (ORCPT ); Sat, 24 Feb 2018 17:17:28 -0500 Received: from mga04.intel.com ([192.55.52.120]:23057 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751399AbeBXWR0 (ORCPT ); Sat, 24 Feb 2018 17:17:26 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.47,389,1515484800"; d="scan'208";a="20564903" From: Sai Praneeth Prakhya To: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Sai Praneeth , "Lee, Chun-Yi" , Borislav Petkov , Tony Luck , Will Deacon , Dave Hansen , Mark Rutland , Bhupesh Sharma , Ricardo Neri , Ravi Shankar , Matt Fleming , Peter Zijlstra , Ard Biesheuvel , Dan Williams Subject: [PATCH V1 0/3] Use efi_rts_workqueue to invoke EFI Runtime Services Date: Sat, 24 Feb 2018 14:10:46 -0800 Message-Id: <1519510249-31447-1-git-send-email-sai.praneeth.prakhya@intel.com> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Sai Praneeth This patch set is an outcome of the discussion at https://lkml.org/lkml/2017/8/21/607 Presently, efi_runtime_services() are executed by firmware in process context. To execute efi_runtime_service(), kernel switches the page directory from swapper_pgd to efi_pgd. However, efi_pgd doesn't have any user space mappings. A potential issue could be, for instance, an NMI interrupt (like perf) trying to profile some user data while in efi_pgd. A solution for this issue could be to use kthread to run efi_runtime_service(). When a user/kernel thread requests to execute efi_runtime_service(), kernel off-loads this work to kthread which in turn uses efi_pgd. Anything that tries to touch user space addresses while in kthread is terminally broken. This patch set adds support to the efi subsystem to handle all calls to efi_runtime_services() using a work queue (which in turn uses kthread). Implementation summary: ----------------------- 1. When a user/kernel thread requests to execute efi_runtime_service(), enqueue work to a work queue, efi_rts_workqueue. 2. The caller thread waits until the work is finished because it's dependent on the return status of efi_runtime_service() and, in specific cases, the arguments populated by efi_runtime_service(). Some efi_runtime_services() takes a pointer to buffer as an argument and fills up the buffer with requested data. For instance, efi_get_variable() and efi_get_next_variable(). Hence, the caller process cannot just post the work and get going, it has to wait for results from firmware. Caveat: efi_rts_workqueue to run efi_runtime_services() shouldn't be used while in atomic, because caller thread might sleep. Presently, pstore code doesn't use efi_rts_workqueue. Tested using LUV (Linux UEFI Validation) for x86_64 and x86_32. Builds fine for arm and arm64. Will appreciate the effort if someone could test the patches on ARM (although I was able to boot with LUV for ARM). LUV: https://01.org/linux-uefi-validation Thanks to Ricardo and Dan for initial reviews and suggestions. Please feel free to pour in your comments and concerns. Note: Patches are based on Linus's kernel v4.16-rc2 Sai Praneeth (3): x86/efi: Call efi_delete_dummy_variable() during efi subsystem initialization efi: Introduce efi_rts_workqueue and necessary infrastructure to invoke all efi_runtime_services() efi: Use efi_rts_workqueue to invoke EFI Runtime Services arch/x86/include/asm/efi.h | 1 - arch/x86/platform/efi/efi.c | 6 - drivers/firmware/efi/efi.c | 18 +++ drivers/firmware/efi/runtime-wrappers.c | 229 +++++++++++++++++++++++++++++--- include/linux/efi.h | 26 ++++ 5 files changed, 253 insertions(+), 27 deletions(-) Signed-off-by: Sai Praneeth Prakhya Suggested-by: Andy Lutomirski Cc: Lee, Chun-Yi Cc: Borislav Petkov Cc: Tony Luck Cc: Will Deacon Cc: Dave Hansen Cc: Mark Rutland Cc: Bhupesh Sharma Cc: Ricardo Neri Cc: Ravi Shankar Cc: Matt Fleming Cc: Peter Zijlstra Cc: Ard Biesheuvel Cc: Dan Williams -- 2.1.4