From: Fenghua Yu <fenghua.yu@intel.com>
To: peterz@infradead.org
Cc: Fenghua Yu <fenghua.yu@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
Tony Luck <tony.luck@intel.com>, H Peter Anvin <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
Xiaoyao Li <xiaoyao.li@intel.com>, x86 <x86@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC] x86/bus_lock: Enable bus lock detection
Date: Wed, 29 Jul 2020 20:40:57 +0000 [thread overview]
Message-ID: <20200729204057.GB318595@otcwcpicx6.sc.intel.com> (raw)
In-Reply-To: <20200729084947.GY119549@hirez.programming.kicks-ass.net>
Hi, Peter,
On Wed, Jul 29, 2020 at 10:49:47AM +0200, peterz@infradead.org wrote:
> On Fri, Jul 17, 2020 at 02:35:00PM -0700, Fenghua Yu wrote:
>
> > #DB for bus lock detect fixes all issues in #AC for split lock detect:
> > 1) It's architectural ... just need to look at one CPUID bit to know it
> > exists
> > 2) The IA32_DEBUGCTL MSR, which reports bus lock in #DB, is per-thread.
> > So each process or guest can have different behavior.
>
> And it generates a whole new problem due to #DB being an IST, and
>
> > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> > index b038695f36c5..58725567da39 100644
> > --- a/arch/x86/kernel/traps.c
> > +++ b/arch/x86/kernel/traps.c
> > @@ -812,6 +812,16 @@ static void handle_debug(struct pt_regs *regs, unsigned long dr6, bool user)
> > if (!user && !dr6)
> > return;
> >
> > + /* Handle bus lock. */
> > + if (!(dr6 & DR_BUS_LOCK)) {
> > + cond_local_irq_enable(regs);
> > + if (user)
> > + handle_user_bus_lock(regs);
> > + else
> > + handle_kernel_bus_lock(regs);
> > + goto out;
> > + }
> > +
> > /*
> > * If dr6 has no reason to give us about the origin of this trap,
> > * then it's very likely the result of an icebp/int01 trap.
>
> we very much rely on #DB never recursing, which we carefully crafted by
> disallowing hardare breakpoints on noinstr code and clearing DR7 early.
>
> But now it can... please keep the pieces.
Can we disable Bus Lock Detection before handle it and re-enable it
after handle it? Will that resolve the recursion issue?
Thanks.
-Fenghua
next prev parent reply other threads:[~2020-07-29 20:41 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 21:35 [PATCH RFC] x86/bus_lock: Enable bus lock detection Fenghua Yu
2020-07-29 3:02 ` Sean Christopherson
2020-07-29 8:50 ` peterz
2020-07-29 18:09 ` Yu, Fenghua
2020-07-29 18:46 ` Sean Christopherson
2020-07-29 19:42 ` Fenghua Yu
2020-07-29 20:00 ` Sean Christopherson
2020-07-29 20:09 ` peterz
2020-07-29 20:35 ` Fenghua Yu
2020-07-29 20:39 ` Sean Christopherson
2020-07-29 22:07 ` Fenghua Yu
2020-07-29 23:28 ` Sean Christopherson
2020-07-29 8:49 ` peterz
2020-07-29 20:40 ` Fenghua Yu [this message]
2020-07-29 21:09 ` peterz
2020-07-30 10:08 ` Thomas Gleixner
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