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x86/debug: Change thread.debugreg6 to thread.virtual_dr6

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Current usage of thread.debugreg6 is convoluted at best. It starts life as
a copy of the hardware DR6 value, but then various bits are cleared and
set.

Replace this with a new variable thread.virtual_dr6 that is initialized to
0 when DR6 is read and only gains bits, at the same time the actual (on
stack) dr6 value which is read from the hardware only gets bits cleared.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20200902133201.415372940@infradead.org
This commit is contained in:
Peter Zijlstra
2020-09-02 15:26:02 +02:00
committed by Thomas Gleixner
parent f4956cf83e
commit d53d9bc0cf
5 changed files with 26 additions and 24 deletions
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12
arch/x86/kernel/hw_breakpoint.c
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@@ -454,7 +454,7 @@ void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
t->ptrace_bps[i] = NULL;
}
t->debugreg6 = 0;
t->virtual_dr6 = 0;
t->ptrace_dr7 = 0;
}
@@ -489,8 +489,8 @@ static int hw_breakpoint_handler(struct die_args *args)
{
int i, rc = NOTIFY_STOP;
struct perf_event *bp;
unsigned long dr6;
unsigned long *dr6_p;
unsigned long dr6;
/* The DR6 value is pointed by args->err */
dr6_p = (unsigned long *)ERR_PTR(args->err);
@@ -504,12 +504,6 @@ static int hw_breakpoint_handler(struct die_args *args)
if ((dr6 & DR_TRAP_BITS) == 0)
return NOTIFY_DONE;
/*
* Reset the DRn bits in the virtualized register value.
* The ptrace trigger routine will add in whatever is needed.
*/
current->thread.debugreg6 &= ~DR_TRAP_BITS;
/* Handle all the breakpoints that were triggered */
for (i = 0; i < HBP_NUM; ++i) {
if (likely(!(dr6 & (DR_TRAP0 << i))))
@@ -554,7 +548,7 @@ static int hw_breakpoint_handler(struct die_args *args)
* breakpoints (to generate signals) and b) when the system has
* taken exception due to multiple causes
*/
if ((current->thread.debugreg6 & DR_TRAP_BITS) ||
if ((current->thread.virtual_dr6 & DR_TRAP_BITS) ||
(dr6 & (~DR_TRAP_BITS)))
rc = NOTIFY_DONE;