[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v4 1/2] xen: EXPERT clean-up and introduce UNSUPPORTED

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
  • Date: Tue, 26 Jan 2021 11:06:17 +0000
  • Accept-language: en-GB, en-US
  • Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=arm.com; dmarc=pass action=none header.from=arm.com; dkim=pass header.d=arm.com; arc=none
  • Arc-message-signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=1MPQXDASd9pvLvWQ9AvBmvIXbuqMuS+G7+m13q15wK4=; b=h6Mzg08Oq8aFd/Ea9TpIpkVf4dxgKm9/v39gyApGpfa8kWdyKfa4fAR2m4LW4iI5yPLyN7ObBRo3fUgCLW1ILhw3wyn3UQKvkLD3NaSlrI1BAnvbecsPTzvH04H2ETP3x08Kalc9Bm8FdIWvATiKr2UEnsR/KHYlIGquru9/6VNN9kMlWnVmbSf6tn70StU88CXxB1ZynYF1SBr0FottYj2eBwWvMElMQYDv1whQpW1TxxBSbuVvBLu1r1M9T9bckrOSMfV9wO9pAHVCMLLToSHc4K5xoKaQwHIijSs0qiSlyTuwXnHAPG/XKPNItFkcD7r3OmIKw7vWAM/6ydQeRQ==
  • Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=ZWhwQNVUeqgPWSjdUIfQPpRIdifeGYNDbYfr6fAD9AqvgzTanGWuTzRerVmW/rSpdDHStpKGFNWB+4B6nsNs5ISmbm68SFtXjCha99C+/zlktfdcysSjLnGAGkmg+aWb24CxCr96vmNzcstZKp7ZbDO1MfGmLd1oPpdjQaTHAHsSQyfl6Eer7ttBQFe7jo3QUR4fqH8EHHm2Yby9H0KzNIc60c9mk2TmnGj3tCBUmG7VeZyU/dPOnNJ+IntHQENaFhxL+N1vakTjSbCffeVqTYb8TYMYLmiQlxpVjt2ZxagwVcq6WjReykpeC2bY/JTswpsCvrEo2tZa31X9EdUyMg==
  • Authentication-results-original: suse.com; dkim=none (message not signed) header.d=none;suse.com; dmarc=none action=none header.from=arm.com;
  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>, "andrew.cooper3@xxxxxxxxxx" <andrew.cooper3@xxxxxxxxxx>, "george.dunlap@xxxxxxxxxx" <george.dunlap@xxxxxxxxxx>, "iwj@xxxxxxxxxxxxxx" <iwj@xxxxxxxxxxxxxx>, "julien@xxxxxxx" <julien@xxxxxxx>, "wl@xxxxxxx" <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 26 Jan 2021 11:06:37 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Nodisclaimer: true
  • Original-authentication-results: suse.com; dkim=none (message not signed) header.d=none;suse.com; dmarc=none action=none header.from=arm.com;
  • Thread-index: AQHW82EN9R2ynrmbqk6EAVX0Oyalkao5otWAgAAc8QA=
  • Thread-topic: [PATCH v4 1/2] xen: EXPERT clean-up and introduce UNSUPPORTED


> On 26 Jan 2021, at 09:22, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> On 25.01.2021 22:27, Stefano Stabellini wrote:
>> A recent thread [1] has exposed a couple of issues with our current way
>> of handling EXPERT.
>> 1) It is not obvious that "Configure standard Xen features (expert
>> users)" is actually the famous EXPERT we keep talking about on xen-devel
>> 2) It is not obvious when we need to enable EXPERT to get a specific
>> feature
>> In particular if you want to enable ACPI support so that you can boot
>> Xen on an ACPI platform, you have to enable EXPERT first. But searching
>> through the kconfig menu it is really not clear (type '/' and "ACPI"):
>> nothing in the description tells you that you need to enable EXPERT to
>> get the option.
>> So this patch makes things easier by doing two things:
>> - introduce a new kconfig option UNSUPPORTED which is clearly to enable
>>  UNSUPPORTED features as defined by SUPPORT.md
>> - change EXPERT options to UNSUPPORTED where it makes sense: keep
>>  depending on EXPERT for features made for experts
>> - tag unsupported features by adding (UNSUPPORTED) to the one-line
>>  description
>> - clarify the EXPERT one-line description
>> [1] https://marc.info/?l=xen-devel&m=160333101228981
>> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Answering to Jan...

> Non-Arm bits
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> However, I have questions on the Arm ones (sorry for not noticing
> earlier, as I assume it was this way before already):
>> @@ -77,7 +77,7 @@ config SBSA_VUART_CONSOLE
>>        SBSA Generic UART implements a subset of ARM PL011 UART.
>> config ARM_SSBD
>> -    bool "Speculative Store Bypass Disable" if EXPERT
>> +    bool "Speculative Store Bypass Disable (UNSUPPORTED)" if UNSUPPORTED
>>      depends on HAS_ALTERNATIVE
>>      default y
>>      help
>> @@ -87,7 +87,7 @@ config ARM_SSBD
>>        If unsure, say Y.
>> -    bool "Harden the branch predictor against aliasing attacks" if EXPERT
>> +    bool "Harden the branch predictor against aliasing attacks 
>>      default y
>>      help
>>        Speculation attacks against some high-performance processors rely on
> Both of these default to y and have their _prompt_
> conditional upon EXPERT. Which means only an expert can turn them
> _off_. Which doesn't make it look like these are unsupported? Or
> if anything, turning them off is unsupported?

...You could see that as EXPERT/UNSUPPORTED options can only be
 “modified” from their default value if EXPERT/UNSUPPORTED is activated.
So I find the current solution ok.

If this is a problem we could also change those options to be default to _off_ 
by renaming them to config DISABLE_xxxx


> Jan



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.