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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de, luto@amacapital.net,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	Lai Jiangshan <laijs@linux.alibaba.com>,
	sean.j.christopherson@intel.com, daniel.thompson@linaro.org
Subject: Re: [PATCH 1/6] x86/entry: Introduce local_db_{save,restore}()
Date: Thu, 28 May 2020 22:36:54 +0100	[thread overview]
Message-ID: <8831da5e-b65d-a4e8-2a3b-ac46282f4591@citrix.com> (raw)
In-Reply-To: <20200528211550.GR2483@worktop.programming.kicks-ass.net>

On 28/05/2020 22:15, Peter Zijlstra wrote:
> On Thu, May 28, 2020 at 09:52:30PM +0100, Andrew Cooper wrote:
>> On 28/05/2020 21:19, Peter Zijlstra wrote:
>>> --- a/arch/x86/include/asm/debugreg.h
>>> +++ b/arch/x86/include/asm/debugreg.h
>>> @@ -113,6 +113,31 @@ static inline void debug_stack_usage_inc
>>>  static inline void debug_stack_usage_dec(void) { }
>>>  #endif /* X86_64 */
>>>  
>>> +static __always_inline void local_db_save(unsigned long *dr7)
>>> +{
>>> +	get_debugreg(*dr7, 7);
>>> +	if (*dr7)
>>> +		set_debugreg(0, 7);
>> %dr7 has an architecturally stuck bit in it.
>>
>> You want *dr7 != 0x400 to avoid writing 0 unconditionally.
> Do we have to have that bit set when writing it? Otherwise I might
> actually prefer masking it out.

Not currently.  I guess it depends on how likely %dr7 is to gain an
inverted polarity bit like %dr6 did.

~Andrew

  parent reply	other threads:[~2020-05-28 21:37 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28 20:19 [PATCH 0/6] x86/entry: disallow #DB more Peter Zijlstra
2020-05-28 20:19 ` [PATCH 1/6] x86/entry: Introduce local_db_{save,restore}() Peter Zijlstra
2020-05-28 20:52   ` Andrew Cooper
2020-05-28 21:15     ` Peter Zijlstra
2020-05-28 21:33       ` Peter Zijlstra
2020-05-29 17:28         ` Andy Lutomirski
2020-05-29 19:02           ` Peter Zijlstra
2020-05-28 21:36       ` Andrew Cooper [this message]
2020-05-28 20:19 ` [PATCH 2/6] x86/entry, nmi: Disable #DB Peter Zijlstra
2020-05-28 20:19 ` [PATCH 3/6] x86/entry, mce: Disallow #DB during #MC Peter Zijlstra
2020-05-28 20:19 ` [PATCH 4/6] x86/entry: Optimize local_db_save() for virt Peter Zijlstra
2020-05-29 17:24   ` Sean Christopherson
2020-05-28 20:19 ` [PATCH 5/6] x86/entry: Remove debug IDT frobbing Peter Zijlstra
2020-05-28 20:19 ` [RFC][PATCH 6/6] x86/entry: Remove DBn stacks Peter Zijlstra
2020-05-28 22:35   ` Lai Jiangshan
2020-05-28 22:37     ` Peter Zijlstra
2020-05-28 22:42 ` [PATCH 0/6] x86/entry: disallow #DB more Lai Jiangshan
2020-05-28 22:48   ` Peter Zijlstra
2020-05-28 23:05     ` Lai Jiangshan
2020-05-29  8:00       ` Peter Zijlstra

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