From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A6FE332AABD; Wed, 2 Sep 2026 01:37:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788313032; cv=none; b=XvpyCDF87ZeJHOiY0vFUvZ+vVv/ELg483dVGmtmyGUpiwmLrfj4H68hDGcN5g19RX9LHsz7v4TCcFvt7J846/e25VVvHRRDFqiRqOVu+mWfZJgDX/Dtfjxmog5wJCRDoMvOOADo9NYHIT+80D3MgOwCIDjepooZ/1cXlcYUak+g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788313032; c=relaxed/simple; bh=PN/RKMQ+kPhwT9ygUPKFcKa36gH6AWVpNeQGmNbdbOQ=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=AjvkkbbuZbp02Ldekn4EYIN/+CmUtBRfF6d8iOzVweXEYcEtWQLETnHxh/E262piqtQY3EeWCMiL7o/sTj653YbfbFhDuCvAhIXnSk2/+F422IL6LoShT+C1XQF90MVgPAdQO/xMR7/rNicy6yYPfqZ2M2SdbbFVrx+bW1zERzI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=eoY81sTD; arc=none smtp.client-ip=192.198.163.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="eoY81sTD" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1788313028; x=1819849028; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=PN/RKMQ+kPhwT9ygUPKFcKa36gH6AWVpNeQGmNbdbOQ=; b=eoY81sTDNvXWcCZZ8lXDZzNBphUmpztbxdl/0df3iYVgI0+58pILtR38 Jm+EAove+xIqSDr1tOo1VsV/swddMPaqXaFNtv45+eZS/omgjs6K6YY3/ oUpdmPeN8kAO0MDvwUxpvVzB8gk5Ta9PtwkLc4H77Qsf9JE0ibjr7oNS7 9bC2Vfjsc6fcQsrh/8qqgSnZlLymYet4xlpS7YgPi3bGaVhRtvR+GWubW UY9BZQiETn5hdqgkv9WLZo7A0ZksPodKND8/C3V0icR4Y23Xo2PXfh+Lw bTr47njc2eiuGTWhewcepF2yiBpHY/bxWMpHH+OhmGIvMyYlZynXj++Kd A==; X-CSE-ConnectionGUID: njuIIc0UR2a2U9S7QLOW3A== X-CSE-MsgGUID: Z0fci8IBShqRPSnLGhcFxw== X-IronPort-AV: E=McAfee;i="6800,10657,11893"; a="88884656" X-IronPort-AV: E=Sophos;i="6.25,257,1779174000"; d="scan'208";a="88884656" Received: from orviesa004.jf.intel.com ([10.64.159.144]) by fmvoesa109.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Sep 2026 18:37:04 -0700 X-CSE-ConnectionGUID: wT6x8q+fRSCiUrtlkDWiRA== X-CSE-MsgGUID: 4MavFmIiS46ctkQQM1syVw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,257,1779174000"; d="scan'208";a="273035798" Received: from ubuntu.bj.intel.com ([10.238.152.72]) by orviesa004.jf.intel.com with ESMTP; 01 Sep 2026 18:37:01 -0700 From: Jun Miao To: dave.hansen@linux.intel.com, jarkko@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, kai.huang@intel.com Cc: linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, fan.du@intel.com, challvy.tee@gmail.com, jun.miao@intel.com Subject: [PATCH v7] x86/sgx: Report RCU-Tasks quiescent state in EPC sanitization loop Date: Wed, 2 Sep 2026 09:36:53 +0800 Message-Id: <20260902013653.690506-1-jun.miao@intel.com> X-Mailer: git-send-email 2.32.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When the kernel boots from kexec, the EPC pages may have a stale state. The kernel sanitizes all EPC pages to reset them to a clean state before their first use in any enclave. The EPC size could be several GBs and resetting them could take a significant amount of time. Because of that, the kernel performs the reset in a loop through a kernel thread ksgxd() at early boot, and there's a cond_resched() after resetting each EPC page. This is fine in most cases, but becomes a problem when there's other kernel code waiting for an RCU-Tasks grace period but the cond_resched() in ksgxd() never triggers rescheduling. Because cond_resched() doesn't report a quiescent state when it doesn't trigger rescheduling, the thread that is waiting for an RCU-Tasks grace period will wait until all EPC pages are reset. For instance, BPF LSM subsystem can invoke synchronize_rcu_tasks() at kernel boot time. A VM with a large EPC assigned and BPF LSM enabled can take a long time to boot, with a call trace triggered: rcu_tasks_wait_gp: rcu_tasks grace period number 1 (since boot) is 130631 jiffies old. INFO: task systemd:1 blocked for more than 122 seconds. ... task:systemd state:D stack:0 pid:1 tpid:1 ppid:0 flags:0x00000002 Call Trace: ... schedule_timeout+0x157/0x170 wait_for_completion+0x88/0x150 __wait_rcu_gp+0x17e/0x190 synchronize_rcu_tasks_generic+0x64/0x60 ... synchronize_rcu_tasks+0x15/0x20 register_ftrace_direct+0x31f/0x350 ... bpf_trampoline_link_prog+0x33/0x60 bpf_tracing_prog_attach+0x3c5/0x5f0 Replace cond_resched() with cond_resched_tasks_rcu_qs() which explicitly reports quiescent state regardless of whether actual rescheduling is triggered. Resetting all EPC pages in ksgxd() isn't performance critical so the extra cost of cond_resched_tasks_rcu_qs() isn't a problem. Tests showed this reduced the VM kernel boot time from ~50s to ~700ms. Fixes: e7e0545299d8 ("x86/sgx: Initialize metadata for Enclave Page Cache (EPC) sections") Suggested-by: Kai Huang Co-developed-by: Fan Du Signed-off-by: Fan Du Signed-off-by: Jun Miao Tested-by: Challvy Tee Reviewed-by: Kai Huang Reviewed-by: Jarkko Sakkinen Link: https://github.com/systemd/systemd/issues/40423 --- v1 -> v2: - Clarify the RCU Tasks stall root cause. - Use cond_resched_rcu_qs() following the Kai`s suggestion. v2 -> v3: - cee439398933 ("rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs()") v3 -> v4: - Trim down/rewrite changelog following Kai`s suggestion. v4 -> v5: - Change the title, not state the problem directly - Corrected spelling and grammatical errors by Kai - Add "Reviewed-by: Kai Huang" v5 -> v6: - Add the exactly kind of reminder that why cond_resched() does not trigger rescheduling. v6 -> v7: - Based on Dave's suggestion, add Jarkko's tag: Reviewed-by: Jarkko Sakkinen --- arch/x86/kernel/cpu/sgx/main.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c index 4505f808af5e..207e680732a4 100644 --- a/arch/x86/kernel/cpu/sgx/main.c +++ b/arch/x86/kernel/cpu/sgx/main.c @@ -106,7 +106,13 @@ static unsigned long __sgx_sanitize_pages(struct list_head *dirty_page_list) left_dirty++; } - cond_resched(); + /* + * cond_resched() only schedules when TIF_NEED_RESCHED is set. + * During this boot-time loop that condition may not happen for a + * long time, so report an RCU-Tasks quiescent state explicitly. + * Therefore, change cond_resched() to cond_resched_tasks_rcu_qs(). + */ + cond_resched_tasks_rcu_qs(); } list_splice(&dirty, dirty_page_list); -- 2.43.0