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authorPeter Zijlstra <peterz@infradead.org>2020-09-02 15:26:01 +0200
committerThomas Gleixner <tglx@linutronix.de>2020-09-04 15:12:57 +0200
commitf4956cf83ed12271bdbd5b547f3378add72bbffb (patch)
tree38b50d0123e68a5accafd80d13a680383d506695 /arch/x86/kernel/traps.c
parent21d44be7b6ff4c254dc971e2c99d4082dd470afd (diff)
x86/debug: Support negative polarity DR6 bits
DR6 has a whole bunch of bits that have negative polarity; they were architecturally reserved and defined to be 1 and are now getting used. Since they're 1 by default, 0 becomes the signal value. Handle this by xor'ing the read DR6 value by the reserved mask, this will flip them around such that 1 is the signal value (positive polarity). Current Linux doesn't yet support any of these bits, but there's two defined: - DR6[11] Bus Lock Debug Exception (ISEr39) - DR6[16] Restricted Transactional Memory (SDM) Update ptrace_{set,get}_debugreg() to provide/consume the value in architectural polarity. Although afaict ptrace_set_debugreg(6) is pointless, the value is not consumed anywhere. Change hw_breakpoint_restore() to alway write the DR6_RESERVED value to DR6, again, no consumer for that write. Suggested-by: Andrew Cooper <Andrew.Cooper3@citrix.com> 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/20200902133201.354220797@infradead.org
Diffstat (limited to 'arch/x86/kernel/traps.c')
-rw-r--r--arch/x86/kernel/traps.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 1e890010a062..114515b26168 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -745,9 +745,8 @@ static __always_inline unsigned long debug_read_clear_dr6(void)
* Keep it simple: clear DR6 immediately.
*/
get_debugreg(dr6, 6);
- set_debugreg(0, 6);
- /* Filter out all the reserved bits which are preset to 1 */
- dr6 &= ~DR6_RESERVED;
+ set_debugreg(DR6_RESERVED, 6);
+ dr6 ^= DR6_RESERVED; /* Flip to positive polarity */
/*
* The SDM says "The processor clears the BTF flag when it