Re: [PATCH v11 01/11] x86/hw_breakpoints: Make DR7 updates NMI safe
From: Peter Zijlstra <peterz@infradead.org>
Date: 2026-08-03 06:57:53
Also in:
linux-doc, linux-perf-users, lkml
On Sun, Aug 02, 2026 at 05:18:37PM +0900, Masami Hiramatsu (Google) wrote:
From: Jinchao Wang <redacted> Hardware breakpoint installation and removal run with IRQs disabled, but an NMI can still enter the same code through KGDB. The interrupted operation and the NMI can consequently claim the same slot or overwrite each other's DR7 state.
Is KGDB really the only way to trip this? Mostly I think we let KGDB have the pieces if it does something 'funny'.
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index f846c15f21ca..9ef24b55737f 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c@@ -40,6 +40,9 @@ DEFINE_PER_CPU(unsigned long, cpu_dr7); EXPORT_PER_CPU_SYMBOL(cpu_dr7); +/* Sequence number of the per-CPU DR7 state. */ +DEFINE_PER_CPU(unsigned int, cpu_dr7_seq);
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 3c9f60d6ca5a..f55a0cbd5927 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c@@ -532,10 +532,13 @@ enum nmi_states { static DEFINE_PER_CPU(enum nmi_states, nmi_state); static DEFINE_PER_CPU(unsigned long, nmi_cr2); static DEFINE_PER_CPU(unsigned long, nmi_dr7); +static DEFINE_PER_CPU(unsigned int, nmi_dr7_seq);
This is weird, why have two distinct sequence numbers for dr7?