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([172.25.112.68]) by fmsmga001.fm.intel.com with ESMTP; 31 Jul 2023 00:02:06 -0700 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 2e037e01-2f70-11ee-8613-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1690786936; x=1722322936; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=R/F68dINSJ894CWgsWAeNvE3sYeHzSDBLZY+Pavzuys=; b=MwYQYeWgkLy9687TOqWh8rDzU3V+asMVksYj58l1VRT64u+L3rOFHST1 YJLWsx8mqUSfXSkn2g6H4rwR7iepQyIP2Jvl5IPzppSSba1Ynt9Y0HzfB K2t+M8Uw7jz5PSZ57z+1dlFWb2PlTSfh9P29Aac0WUKbNt89yWnlw6xu4 5seqrDkzXkeHBXh+hAxCMt6gwkpyWl1M6eIke/rjBU8GTYciVfzOe7jTV n6sgDbEOyvmHvFGz6GxScaGgdK81/Z5CcGsz/o4V9STQ0dT7nbVvhjWoe TNXmRB1YPmx4icSt6BhN6U4Y4PF5og8nhPTJ4is+9hym1NbjssvyaGMLv g==; X-IronPort-AV: E=McAfee;i="6600,9927,10787"; a="371649141" X-IronPort-AV: E=Sophos;i="6.01,244,1684825200"; d="scan'208";a="371649141" X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.01,202,1684825200"; d="scan'208";a="871543437" From: Xin Li To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org, linux-hyperv@vger.kernel.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org Cc: Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , Andy Lutomirski , Oleg Nesterov , Tony Luck , "K . Y . Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Sean Christopherson , Peter Zijlstra , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Josh Poimboeuf , "Paul E . McKenney" , Catalin Marinas , Randy Dunlap , Steven Rostedt , Kim Phillips , Xin Li , Hyeonggon Yoo <42.hyeyoo@gmail.com>, "Liam R . Howlett" , Sebastian Reichel , "Kirill A . Shutemov" , Suren Baghdasaryan , Pawan Gupta , Jiaxi Chen , Babu Moger , Jim Mattson , Sandipan Das , Lai Jiangshan , Hans de Goede , Reinette Chatre , Daniel Sneddon , Breno Leitao , Nikunj A Dadhania , Brian Gerst , Sami Tolvanen , Alexander Potapenko , Andrew Morton , Arnd Bergmann , "Eric W . Biederman" , Kees Cook , Masami Hiramatsu , Masahiro Yamada , Ze Gao , Fei Li , Conghui , Ashok Raj , "Jason A . Donenfeld" , Mark Rutland , Jacob Pan , Jiapeng Chong , Jane Malalane , David Woodhouse , Boris Ostrovsky , Arnaldo Carvalho de Melo , Yantengsi , Christophe Leroy , Sathvika Vasireddy Subject: [PATCH v9 16/36] x86/fred: Allow single-step trap and NMI when starting a new task Date: Sun, 30 Jul 2023 23:32:57 -0700 Message-Id: <20230731063317.3720-17-xin3.li@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230731063317.3720-1-xin3.li@intel.com> References: <20230731063317.3720-1-xin3.li@intel.com> MIME-Version: 1.0 From: "H. Peter Anvin (Intel)" Entering a new task is logically speaking a return from a system call (exec, fork, clone, etc.). As such, if ptrace enables single stepping a single step exception should be allowed to trigger immediately upon entering user space. This is not optional. NMI should *never* be disabled in user space. As such, this is an optional, opportunistic way to catch errors. Allow single-step trap and NMI when starting a new task, thus once the new task enters user space, single-step trap and NMI are both enabled immediately. Signed-off-by: H. Peter Anvin (Intel) Tested-by: Shan Kang Signed-off-by: Xin Li --- Changes since v8: * Use high-order 48 bits above the lowest 16 bit SS only when FRED is enabled (Thomas Gleixner). --- arch/x86/kernel/process_64.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 6d5fed29f552..0b47871a6141 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -56,6 +56,7 @@ #include #include #include +#include #ifdef CONFIG_IA32_EMULATION /* Not included via unistd.h */ #include @@ -507,8 +508,18 @@ void x86_gsbase_write_task(struct task_struct *task, unsigned long gsbase) static void start_thread_common(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp, - unsigned int _cs, unsigned int _ss, unsigned int _ds) + u16 _cs, u16 _ss, u16 _ds) { + /* + * Paranoia: High-order 48 bits above the lowest 16 bit SS are + * discarded by the legacy IRET instruction on all Intel, AMD, + * and Cyrix/Centaur/VIA CPUs, thus can be set unconditionally, + * even when FRED is not enabled. But we choose the safer side + * to use these bits only when FRED is enabled. + */ + const unsigned long ssx_flags = cpu_feature_enabled(X86_FEATURE_FRED) ? + (FRED_SSX_SOFTWARE_INITIATED | FRED_SSX_NMI) : 0; + WARN_ON_ONCE(regs != current_pt_regs()); if (static_cpu_has(X86_BUG_NULL_SEG)) { @@ -522,11 +533,11 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip, loadsegment(ds, _ds); load_gs_index(0); - regs->ip = new_ip; - regs->sp = new_sp; - regs->cs = _cs; - regs->ss = _ss; - regs->flags = X86_EFLAGS_IF; + regs->ip = new_ip; + regs->sp = new_sp; + regs->csx = _cs; + regs->ssx = _ss | ssx_flags; + regs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED; } void