Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756110AbZFBWpH (ORCPT ); Tue, 2 Jun 2009 18:45:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755375AbZFBWns (ORCPT ); Tue, 2 Jun 2009 18:43:48 -0400 Received: from fg-out-1718.google.com ([72.14.220.157]:20851 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754869AbZFBWnq (ORCPT ); Tue, 2 Jun 2009 18:43:46 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=from:to:cc:subject:date:message-id:x-mailer:in-reply-to:references; b=aRCypLodWcJkSLKIZAvsMsucdHcRKeDovUrHnkXHE9wlDN2tRz2IexjDym3Mj/zrEN nsKEln6ZXCGYP8K/zDFy0/9h5A73ZbkbT/hv6guGZxrFXV61wBue0+TvG0A0Ty/GP07U ia12IhR3oBuOo8UayOESP9oXcfrAsIFaEr3IE= From: Frederic Weisbecker To: Ingo Molnar Cc: LKML , "K.Prasad" , Steven Rostedt , Alan Stern , Frederic Weisbecker Subject: [PATCH 06/12] hw-breakpoints: use the new wrapper routines to access debug registers in process/thread code Date: Wed, 3 Jun 2009 00:43:30 +0200 Message-Id: <1243982616-18212-7-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.6.2.3 In-Reply-To: <1243982616-18212-1-git-send-email-fweisbec@gmail.com> References: <1243982616-18212-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7750 Lines: 221 From: K.Prasad This patch enables the use of abstract debug registers in process-handling routines, according to the new hardware breakpoint Api. [ Impact: adapt thread breakpoints handling code to the new breakpoint Api ] Original-patch-by: Alan Stern Signed-off-by: K.Prasad Reviewed-by: Alan Stern Signed-off-by: Frederic Weisbecker --- arch/x86/kernel/process.c | 22 ++++++---------------- arch/x86/kernel/process_32.c | 28 ++++++++++++++++++++++++++++ arch/x86/kernel/process_64.c | 31 +++++++++++++++++++++++++++++++ 3 files changed, 65 insertions(+), 16 deletions(-) diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 291527c..19a686c 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -15,6 +15,8 @@ #include #include #include +#include +#include unsigned long idle_halt; EXPORT_SYMBOL(idle_halt); @@ -46,6 +48,8 @@ void free_thread_xstate(struct task_struct *tsk) kmem_cache_free(task_xstate_cachep, tsk->thread.xstate); tsk->thread.xstate = NULL; } + if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG))) + flush_thread_hw_breakpoint(tsk); WARN(tsk->thread.ds_ctx, "leaking DS context\n"); } @@ -106,12 +110,8 @@ void flush_thread(void) clear_tsk_thread_flag(tsk, TIF_DEBUG); - tsk->thread.debugreg[0] = 0; - tsk->thread.debugreg[1] = 0; - tsk->thread.debugreg[2] = 0; - tsk->thread.debugreg[3] = 0; - tsk->thread.debugreg6 = 0; - tsk->thread.debugreg7 = 0; + if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG))) + flush_thread_hw_breakpoint(tsk); memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array)); /* * Forget coprocessor state.. @@ -193,16 +193,6 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p, else if (next->debugctlmsr != prev->debugctlmsr) update_debugctlmsr(next->debugctlmsr); - if (test_tsk_thread_flag(next_p, TIF_DEBUG)) { - set_debugreg(next->debugreg[0], 0); - set_debugreg(next->debugreg[1], 1); - set_debugreg(next->debugreg[2], 2); - set_debugreg(next->debugreg[3], 3); - /* no 4 and 5 */ - set_debugreg(next->debugreg6, 6); - set_debugreg(next->debugreg7, 7); - } - if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^ test_tsk_thread_flag(next_p, TIF_NOTSC)) { /* prev and next are different */ diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index b5e4bfe..297ffff 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -61,6 +61,8 @@ #include #include #include +#include +#include asmlinkage void ret_from_fork(void) __asm__("ret_from_fork"); @@ -265,7 +267,13 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, task_user_gs(p) = get_user_gs(regs); + p->thread.io_bitmap_ptr = NULL; tsk = current; + err = -ENOMEM; + if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG))) + if (copy_thread_hw_breakpoint(tsk, p, clone_flags)) + goto out; + if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) { p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr, IO_BITMAP_BYTES, GFP_KERNEL); @@ -285,10 +293,13 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, err = do_set_thread_area(p, -1, (struct user_desc __user *)childregs->si, 0); +out: if (err && p->thread.io_bitmap_ptr) { kfree(p->thread.io_bitmap_ptr); p->thread.io_bitmap_max = 0; } + if (err) + flush_thread_hw_breakpoint(p); clear_tsk_thread_flag(p, TIF_DS_AREA_MSR); p->thread.ds_ctx = NULL; @@ -427,6 +438,23 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) lazy_load_gs(next->gs); percpu_write(current_task, next_p); + /* + * There's a problem with moving the arch_install_thread_hw_breakpoint() + * call before current is updated. Suppose a kernel breakpoint is + * triggered in between the two, the hw-breakpoint handler will see that + * the 'current' task does not have TIF_DEBUG flag set and will think it + * is leftover from an old task (lazy switching) and will erase it. Then + * until the next context switch, no user-breakpoints will be installed. + * + * The real problem is that it's impossible to update both current and + * physical debug registers at the same instant, so there will always be + * a window in which they disagree and a breakpoint might get triggered. + * Since we use lazy switching, we are forced to assume that a + * disagreement means that current is correct and the exception is due + * to lazy debug register switching. + */ + if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG))) + arch_install_thread_hw_breakpoint(next_p); return prev_p; } diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 5a1a1de..f7b276d 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -55,6 +55,8 @@ #include #include #include +#include +#include asmlinkage extern void ret_from_fork(void); @@ -248,6 +250,8 @@ void release_thread(struct task_struct *dead_task) BUG(); } } + if (unlikely(dead_task->thread.debugreg7)) + flush_thread_hw_breakpoint(dead_task); } static inline void set_32bit_tls(struct task_struct *t, int tls, u32 addr) @@ -303,12 +307,18 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, p->thread.fs = me->thread.fs; p->thread.gs = me->thread.gs; + p->thread.io_bitmap_ptr = NULL; savesegment(gs, p->thread.gsindex); savesegment(fs, p->thread.fsindex); savesegment(es, p->thread.es); savesegment(ds, p->thread.ds); + err = -ENOMEM; + if (unlikely(test_tsk_thread_flag(me, TIF_DEBUG))) + if (copy_thread_hw_breakpoint(me, p, clone_flags)) + goto out; + if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) { p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL); if (!p->thread.io_bitmap_ptr) { @@ -347,6 +357,9 @@ out: kfree(p->thread.io_bitmap_ptr); p->thread.io_bitmap_max = 0; } + if (err) + flush_thread_hw_breakpoint(p); + return err; } @@ -492,6 +505,24 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) */ if (tsk_used_math(next_p) && next_p->fpu_counter > 5) math_state_restore(); + /* + * There's a problem with moving the arch_install_thread_hw_breakpoint() + * call before current is updated. Suppose a kernel breakpoint is + * triggered in between the two, the hw-breakpoint handler will see that + * the 'current' task does not have TIF_DEBUG flag set and will think it + * is leftover from an old task (lazy switching) and will erase it. Then + * until the next context switch, no user-breakpoints will be installed. + * + * The real problem is that it's impossible to update both current and + * physical debug registers at the same instant, so there will always be + * a window in which they disagree and a breakpoint might get triggered. + * Since we use lazy switching, we are forced to assume that a + * disagreement means that current is correct and the exception is due + * to lazy debug register switching. + */ + if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG))) + arch_install_thread_hw_breakpoint(next_p); + return prev_p; } -- 1.6.2.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/