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Mon, 12 Apr 2021 15:51:19 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 469AEB317; Mon, 12 Apr 2021 15:51:18 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 07ebdc7f-00d7-4b53-89cc-fc8fe4beda37 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1618242678; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ySzFyc2m+/hF5QuiGBCAs6tV9dvl6k34txaxGc4Ri7Y=; b=hoRfPgcrSFTW/gKUPo1Nwjegb53qSEWZmjU92mGry0y8gzRhn7ej1yDcw3xepgIOnyiW5+ CvqQt5L5Zy1Xp9pI2cA5P3IGn6JDCQllad5f8qk35q3D9fE10iIWLm4Gdq845B8QDdul0K eNkvltxPHJdeGoPbWzGnhUpyYQj3nVY= Subject: Re: [PATCH 1/2] x86: correct is_pv_domain() when !CONFIG_PV To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Wei Liu References: <7c040eff-2746-59e3-b657-64f5df3c9085@suse.com> <54013074-1fc4-1047-0d00-2762fcbc9ade@suse.com> <169d6a5b-81ec-f347-8edc-60ba6ab0864f@suse.com> <9571d2ac-e8ae-4105-5f92-0a81728f44d2@suse.com> From: Jan Beulich Message-ID: Date: Mon, 12 Apr 2021 17:51:17 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 12.04.2021 17:40, Roger Pau Monné wrote: > On Mon, Apr 12, 2021 at 05:24:41PM +0200, Jan Beulich wrote: >> On 12.04.2021 16:49, Roger Pau Monné wrote: >>> On Mon, Apr 12, 2021 at 12:07:12PM +0200, Jan Beulich wrote: >>>> On 12.04.2021 11:34, Roger Pau Monné wrote: >>>>> On Fri, Nov 27, 2020 at 05:54:57PM +0100, Jan Beulich wrote: >>>>>> --- a/xen/include/xen/sched.h >>>>>> +++ b/xen/include/xen/sched.h >>>>>> @@ -985,7 +985,7 @@ static always_inline bool is_control_dom >>>>>> >>>>>> static always_inline bool is_pv_domain(const struct domain *d) >>>>>> { >>>>>> - return IS_ENABLED(CONFIG_PV) && >>>>>> + return IS_ENABLED(CONFIG_X86) && >>>>>> evaluate_nospec(!(d->options & XEN_DOMCTL_CDF_hvm)); >>>>>> } >>>>>> >>>>>> @@ -1011,7 +1011,7 @@ static always_inline bool is_pv_32bit_vc >>>>>> >>>>>> static always_inline bool is_pv_64bit_domain(const struct domain *d) >>>>>> { >>>>>> - if ( !is_pv_domain(d) ) >>>>>> + if ( !IS_ENABLED(CONFIG_PV) || !is_pv_domain(d) ) >>>>>> return false; >>>>> >>>>> I think overall is confusing to have a domain that returns true for >>>>> is_pv_domain but false for both is_pv_{64,32}bit_domain checks. >>>>> >>>>> I know those are only the system domains, but it feels confusing and >>>>> could cause mistakes in the future IMO, as then we would have to >>>>> carefully think where to use ( is_pv_64bit_domain(d) >>>>> || is_pv_32bit_domain(d) ) vs just using is_pv_domain(d), or >>>>> IS_ENABLED(CONFIG_PV) && is_pv_domain(d) >>>> >>>> Imo it's not "then we would have to carefully think where to use ..." >>>> but instead this patch is an indication that we should have been for >>>> quite some time. For this reason (coming back to your first comment >>>> at the top) I'm not sure adding a comment _there_ is actually useful. >>>> Every use of is_pv_*() needs carefully considering which domains are >>>> really meant. >>> >>> Maybe we shouldn't have used is_pv_domain as a way to hide code from >>> the compiler and instead always provide dummy functions, as even with >>> PV support compiled out we still need some of it for system domains. >>> >>> I'm not sure I have a good proposal to make, but it seems wrong to me >>> that is_pv_domain(d) could be different than is_pv_64bit_domain(d) || >>> is_pv_32bit_domain(d). >> >> Hmm, so we're of opposite opinions - not sure what to do. Short of >> having / introducing is_system_domain() or some such (with all the >> needed auditing) I can't see how assuming the two would mean the >> same could ever have been true. With what we have is_pv_domain() is >> legitimately true for them, and both is_pv_{32,64}bit_domain() ought >> to be false (as there's no specific bitness associated with them) >> imo _at least_ when !PV. > > It's all quite ugly, but I wasn't really getting your reasoning that > system domains can be considered PV domains without a bitness. > > I think we both agree that long term having is_system_domain would be > the cleanest solution, but it needs a lot of auditing. Yes. > I think I would > be fine if you could add a comment somewhere noting that system > domains can be identified as PV domains without a bitness, so that > it's likely less confusing in the future. I've added /* * Note that is_pv_domain() can return true (for system domains) even when * both is_pv_64bit_domain() and is_pv_32bit_domain() return false. IOW * system domains can be considered PV without specific bitness. */ immediately ahead of is_pv_domain(). Does this sound okay? Jan