Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf

From: "Jürgen Groß" <jgross@suse.com>
To: Mark Rutland <mark.rutland@arm.com>, Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	"VMware, Inc." <pv-drivers@vmware.com>, X86 ML <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf
Date: Wed, 9 Dec 2020 15:05:39 +0100	[thread overview]
Message-ID: <a37be173-6702-5523-8757-2b5a1b4ae311@suse.com> (raw)
In-Reply-To: <20201209140221.GA9087@C02TD0UTHF1T.local>

[-- Attachment #1.1.1: Type: text/plain, Size: 2078 bytes --]

On 09.12.20 15:02, Mark Rutland wrote:
> On Wed, Dec 09, 2020 at 01:27:10PM +0000, Mark Rutland wrote:
>> On Sun, Nov 22, 2020 at 01:44:53PM -0800, Andy Lutomirski wrote:
>>> On Sat, Nov 21, 2020 at 10:55 PM Jürgen Groß <jgross@suse.com> wrote:
>>>> On 20.11.20 12:59, Peter Zijlstra wrote:
>>>>> If someone were to write horrible code like:
>>>>>
>>>>>        local_irq_disable();
>>>>>        local_irq_save(flags);
>>>>>        local_irq_enable();
>>>>>        local_irq_restore(flags);
>>>>>
>>>>> we'd be up some creek without a paddle... now I don't _think_ we have
>>>>> genius code like that, but I'd feel saver if we can haz an assertion in
>>>>> there somewhere...
> 
>> I was just talking to Peter on IRC about implementing the same thing for
>> arm64, so could we put this in the generic irqflags code? IIUC we can
>> use raw_irqs_disabled() to do the check.
>>
>> As this isn't really entry specific (and IIUC the cases this should
>> catch would break lockdep today), maybe we should add a new
>> DEBUG_IRQFLAGS for this, that DEBUG_LOCKDEP can also select?
>>
>> Something like:
>>
>> #define local_irq_restore(flags)                               \
>>         do {                                                    \
>>                 if (!raw_irqs_disabled_flags(flags)) {          \
>>                         trace_hardirqs_on();                    \
>>                 } else if (IS_ENABLED(CONFIG_DEBUG_IRQFLAGS) {  \
>>                         if (unlikely(raw_irqs_disabled())       \
> 
> Whoops; that should be !raw_irqs_disabled().
> 
>>                                 warn_bogus_irqrestore();        \
>>                 }                                               \
>>                 raw_local_irq_restore(flags);                   \
>>          } while (0)
>>
>> ... perhaps? (ignoring however we deal with once-ness).
> 
> If no-one shouts in the next day or two I'll spin this as its own patch.

Fine with me. So I'll just ignore a potential error case in my patch.

Thanks,

Juergen

[-- Attachment #1.1.2: OpenPGP_0xB0DE9DD628BF132F.asc --]
[-- Type: application/pgp-keys, Size: 3135 bytes --]

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 495 bytes --]