From: Josh Poimboeuf <jpoimboe@redhat.com>
To: speck@linutronix.de
Subject: [MODERATED] Re: [PATCH v4 04/10] TAAv4 4
Date: Wed, 25 Sep 2019 17:58:31 -0500 [thread overview]
Message-ID: <20190925225831.a2krvh274t63sjqe@treble> (raw)
In-Reply-To: <00170736-0d97-4a48-2141-ffba4bb67199@intel.com>
On Mon, Sep 09, 2019 at 08:42:54AM -0700, speck for Dave Hansen wrote:
> >>> +static void tsx_update_this_cpu(void *arg)
> >>> +{
> >>> + struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
> >>> + unsigned long enable = (unsigned long)arg;
> >>> +
> >>> + if (enable) {
> >>> + tsx_enable();
> >>> + set_cpu_cap(c, X86_FEATURE_RTM);
> >>> + } else {
> >>> + tsx_disable();
> >>> + clear_cpu_cap(c, X86_FEATURE_RTM);
> >>> + }
> >>> +}
> >>
> >> This makes me really nervous.
> >>
> >> Do we have any other *runtime* (after early boot) manipulation of
> >> X86_FEATURE_* flags?
> >
> > I don't think we have an option. TSX_CTRL MSR write would change the
> > CPUID anyways. It is probably better to have X86_FEATURE_RTM reflect
> > the correct state.
>
> We have a choice.
>
> If we don't have the infrastructure to do something right, we don't do
> it. Poking at the bits and praying nothing breaks is not my preferred
> approach. Could you please take a look and try to answer my question:
>
> Do we have any other *runtime* (after early boot) manipulation
> of X86_FEATURE_* flags?
>
> If the answer is no, then there's some homework that needs to be done to
> see what the implications are here and to make sure that nothing will
> break. From the changelog and comments, it appears that research hasn't
> been done.
Right. This patch feels dangerous and fragile...
And what's the point anyway? There's hardly any justification in the
patch description. Is it a theoretical problem or is there a real-world
production use case?
Please drop this patch, or at least, put it at the very end of the set.
--
Josh
next prev parent reply other threads:[~2019-09-25 22:58 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1567543894.git.pawan.kumar.gupta@linux.intel.com>
2019-09-23 12:47 ` [MODERATED] Re: [PATCH v4 01/10] TAAv4 1 Borislav Petkov
[not found] ` <20190904060028.GD7212@kroah.com>
[not found] ` <20190906072835.GD13480@guptapadev.amr>
[not found] ` <20190906092727.GA16843@kroah.com>
[not found] ` <20190910184223.GA7543@guptapadev.amr>
[not found] ` <20190910223334.GA21301@kroah.com>
[not found] ` <20190910233449.GA10041@agluck-desk2.amr.corp.intel.com>
2019-09-23 19:10 ` [MODERATED] Re: [PATCH v4 04/10] TAAv4 4 Greg KH
[not found] ` <20190911023223.GA8305@guptapadev.amr>
2019-09-23 19:13 ` Greg KH
2019-09-23 22:25 ` Pawan Gupta
2019-09-24 5:04 ` Greg KH
2019-09-24 10:48 ` Jiri Kosina
2019-09-24 13:31 ` Greg KH
2019-09-24 13:38 ` Jiri Kosina
2019-09-24 13:47 ` Greg KH
2019-09-24 23:25 ` Pawan Gupta
2019-09-27 7:01 ` Greg KH
2019-09-25 21:10 ` [MODERATED] Re: [PATCH v4 06/10] TAAv4 6 Kanth Ghatraju
2019-09-25 21:11 ` [MODERATED] [AUTOREPLY] [AUTOREPLY] Automatic reply: " Hatle, Mark
2019-09-26 1:15 ` [MODERATED] " Pawan Gupta
[not found] ` <20190904055711.GC7212@kroah.com>
[not found] ` <nycvar.YFH.7.76.1909040759580.31470@cbobk.fhfr.pm>
[not found] ` <20190904061155.GI7212@kroah.com>
[not found] ` <20190904075846.GD1321@guptapadev.amr>
[not found] ` <20190904084306.GA4925@kroah.com>
[not found] ` <20190904112758.GP3838@dhcp22.suse.cz>
2019-09-25 22:05 ` [MODERATED] Re: ***UNCHECKED*** Re: [PATCH v4 03/10] TAAv4 3 Josh Poimboeuf
2019-10-01 0:20 ` [MODERATED] " Pawan Gupta
2019-10-02 14:55 ` Borislav Petkov
2019-10-05 5:16 ` Pawan Gupta
2019-10-08 2:59 ` Josh Poimboeuf
2019-10-08 6:15 ` Pawan Gupta
2019-10-08 18:06 ` Dave Hansen
2019-10-08 18:36 ` [MODERATED] Re: ***UNCHECKED*** " Jiri Kosina
[not found] ` <20190904055406.GA7212@kroah.com>
[not found] ` <20190904074326.GB1321@guptapadev.amr>
[not found] ` <bfe6f7e0-22db-ce4d-ac3a-875482b43489@intel.com>
2019-09-25 22:13 ` [MODERATED] Re: [PATCH v4 02/10] TAAv4 2 Josh Poimboeuf
2019-09-26 0:46 ` Pawan Gupta
2019-09-25 22:30 ` Josh Poimboeuf
2019-09-30 23:26 ` Pawan Gupta
2019-09-30 23:32 ` [MODERATED] [AUTOREPLY] [MODERATED] [AUTOREPLY] Automatic reply: " James, Hengameh M
[not found] ` <5b6df5ee-a5b7-c281-de29-af6544b8abb6@intel.com>
[not found] ` <20190906074645.GE13480@guptapadev.amr>
2019-09-25 22:48 ` [MODERATED] Re: [PATCH v4 03/10] TAAv4 3 Josh Poimboeuf
2019-09-25 23:12 ` Dave Hansen
2019-09-25 23:22 ` Andrew Cooper
2019-09-26 1:13 ` Pawan Gupta
2019-09-26 2:34 ` Josh Poimboeuf
2019-09-26 7:15 ` Pawan Gupta
2019-09-26 13:54 ` Josh Poimboeuf
2019-09-26 17:57 ` Pawan Gupta
[not found] ` <d6fd9ad7-79f7-aab9-db31-a9a2ca03aa10@intel.com>
[not found] ` <20190906080828.GF13480@guptapadev.amr>
[not found] ` <00170736-0d97-4a48-2141-ffba4bb67199@intel.com>
2019-09-25 22:58 ` Josh Poimboeuf [this message]
2019-09-26 0:48 ` [MODERATED] Re: [PATCH v4 04/10] TAAv4 4 Pawan Gupta
2019-09-25 23:06 ` [MODERATED] Re: [PATCH v4 06/10] TAAv4 6 Josh Poimboeuf
2019-09-30 23:00 ` Pawan Gupta
2019-10-01 18:26 ` [MODERATED] Re: [PATCH v4 05/10] TAAv4 5 Pawan Gupta
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