Re: [PATCH 1/2] x86: report if PCID and INVPCID are supported

From: "Jan Beulich" <JBeulich@suse.com>
To: Wei Liu <wei.liu2@citrix.com>, Juergen Gross <jgross@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH 1/2] x86: report if PCID and INVPCID are supported
Date: Mon, 05 Mar 2018 05:37:38 -0700	[thread overview]
Message-ID: <5A9D482202000078001AE7ED@prv-mh.provo.novell.com> (raw)
In-Reply-To: <fdc238ab-ad02-69a0-0e3a-3c2e643a40e7@suse.com>

>>> On 05.03.18 at 12:43, <jgross@suse.com> wrote:
> On 05/03/18 12:20, Jan Beulich wrote:
>>>>> On 05.03.18 at 10:50, <wei.liu2@citrix.com> wrote:
>>> --- a/xen/arch/x86/setup.c
>>> +++ b/xen/arch/x86/setup.c
>>> @@ -1701,6 +1701,13 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>>>             cpu_has_nx ? XENLOG_INFO : XENLOG_WARNING "Warning: ",
>>>             cpu_has_nx ? "" : "not ");
>>>  
>>> +
>>> +    printk(XENLOG_INFO
>>> +           "PCID (Process-Context IDentifier) %ssupported\n",
>>> +           cpu_has_pcid ? "" : "not ");
>>> +
>>> +    printk(XENLOG_INFO "INVPCID %ssupported\n", cpu_has_invpcid ? "" : "not ");
>> 
>> Do we really need this? We log a message for NX as an exception,
>> we don't do so for other features (and things would get pretty
>> unwieldy if we did).
> 
> I'd rather keep this message. As we are hiding PCID and INPCID from dom0
> this is the only indicator of those features being supported. In case of
> an error related to TLB consistency this information is important IMO.

Well, this argument would hold for almost every other advanced
feature we use.

Jan

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