Messages in this thread | | | Date | Sun, 10 Jan 2010 04:18:58 +0100 | From | Frederic Weisbecker <> | Subject | Re: [RFC Patch 2/2][Bugfix][x86][hw-breakpoint] Fix return-code to notifier chain in hw_breakpoint_handler |
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On Fri, Jan 01, 2010 at 12:32:17AM +0530, K.Prasad wrote: > On Thu, Dec 31, 2009 at 01:38:09AM +0100, Frederic Weisbecker wrote: > > On Sat, Dec 26, 2009 at 11:58:33PM +0530, K.Prasad wrote: > > > The hw-breakpoint handler will return NOTIFY_DONE for user-space breakpoints > > > to generate SIGTRAP signal (and not for kernel-space addresses). > > > > > > Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com> > > > --- > > > arch/x86/kernel/hw_breakpoint.c | 9 +++++++-- > > > 1 file changed, 7 insertions(+), 2 deletions(-) > > > > > > Index: linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c > > > =================================================================== > > > --- linux-2.6-tip.orig/arch/x86/kernel/hw_breakpoint.c > > > +++ linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c > > > @@ -502,8 +502,6 @@ static int __kprobes hw_breakpoint_handl > > > rcu_read_lock(); > > > > > > bp = per_cpu(bp_per_reg[i], cpu); > > > - if (bp) > > > - rc = NOTIFY_DONE; > > > /* > > > * Reset the 'i'th TRAP bit in dr6 to denote completion of > > > * exception handling > > > @@ -517,6 +515,13 @@ static int __kprobes hw_breakpoint_handl > > > rcu_read_unlock(); > > > break; > > > } > > > + /* > > > + * Further processing in do_debug() is needed for a) user-space > > > + * breakpoints (to generate signals) and b) when the system has > > > + * taken exception due to multiple causes > > > + */ > > > + if (bp->attr.bp_addr < TASK_SIZE) > > > + rc = NOTIFY_DONE; > > > > > > perf_bp_event(bp, args->regs); > > > > > > > > > > > > Oh and now that I see this patch, the previous one indeed makes sense > > with this check: > > > > if (dr6 & (~DR_TRAP_BITS)) > > rc = NOTIFY_DONE; > > > > That said, it means thread.debugreg6 won't get the reserved bits anymore. > > I see some use of them from kvm (it restores the reserved bits on guest<->host > > switch). Not sure if this inconsistency could affect kvm... > > > > Can you point me to the relevant code?
I see various uses of DR6_VOLATILE and DR6_FIXED_1 in arch/x86/kvm/, DR6_FIXED_1 being the fixed unused bits in dr6. Not sure how this patch would affect what's set there.
I'll wait for Jan's answer.
Thanks.
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