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From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: speck@linutronix.de
Subject: [MODERATED] Re: [PATCH v4 02/10] TAAv4 2
Date: Wed, 25 Sep 2019 17:46:00 -0700	[thread overview]
Message-ID: <20190926004559.GB16811@guptapadev.amr> (raw)
In-Reply-To: <20190925221319.5h4c3os5ptm6iaft@treble>

On Wed, Sep 25, 2019 at 05:13:19PM -0500, speck for Josh Poimboeuf wrote:
> On Fri, Sep 06, 2019 at 02:07:12PM -0700, speck for Dave Hansen wrote:
> > On 9/4/19 12:43 AM, speck for Pawan Gupta wrote:
> > > On Wed, Sep 04, 2019 at 07:54:06AM +0200, speck for Greg KH wrote:
> > >>> +static void tsx_ctrl_check_support(struct cpuinfo_x86 *c)
> > >>> +{
> > >>> +	u64 ia32_cap = 0;
> > >>> +
> > >>> +	if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
> > >>> +		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
> > >>> +
> > >>> +	if (!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR))
> > >>> +		tsx_ctrl_state = TSX_CTRL_NOT_SUPPORTED;
> > >> Why isn't this if statement under the if statement above?
> > > Because we still have to set tsx_ctrl_state when cpu doesn't support
> > > X86_FEATURE_ARCH_CAPABILITIES.
> > 
> > FWIW, I struggled to read this the first time I read it, too.  It might
> > make sense to break it up like this:
> > 
> > u64 read_ia32_arch_cap(void)
> > {
> > 	u64 ia32_cap = 0;
> > 
> > 	/* Leave the MSR set to all 0's when not supported */
> > 	if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
> > 		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
> > 
> > 	return ia32_cap;
> > }
> > 
> > You could even replace the other places that we read the MSR.  They have
> > the same pattern.  Then do:
> > 
> > static void tsx_ctrl_check_support(struct cpuinfo_x86 *c)
> > {
> > 	u64 ia32_cap = read_ia32_arch_cap();
> > 
> > 	if (ia32_cap & ARCH_CAP_TSX_CTRL_MSR)
> > 		tsx_ctrl_state = TSX_CTRL_ENABLE;
> > }
> > 
> > which takes tsx_ctrl_state out of the 'disable' mode.
> 
> I think it would be even clearer if the compile-time default were
> changed to TSX_CTRL_NOT_SUPPORTED.
> 
> Then the logic would be less confusing.  For example the reader of the
> code doesn't have to remember that ia32_cap is initialized to zero.  And
> IMO, "not supported" conceptually makes the most sense as a compile-time
> default anyway.
> 
> static void tsx_ctrl_check_support(struct cpuinfo_x86 *c)
> {
> 	u64 ia32_cap;
> 
> 	if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES)) {
> 		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
> 
> 		if (ia32_cap & ARCH_CAP_TSX_CTRL_MSR)
> 			tsx_ctrl_state = TSX_CTRL_DISABLE;

Below is the order in which tsx_ctrl_state can be modified:
1. Compile time
2. Cmdline parsing (early_param())
3. TSX_CTRL MSR support check (tsx_ctrl_check_support())

Here we need to handle tsx=on case as well. If we set tsx_ctrl_state to
ENABLE/DISABLE in tsx_ctrl_check_support() we could override what user
asked for via cmdline. Unless we keep another copy of tsx_ctrl_state,
which might add more complexity.

I believe tsx_ctrl_check_support() should only change state to
NOT_SUPPORTED when TSX_CTRL MSR is not supported.

Thanks,
Pawan

  reply	other threads:[~2019-09-26  0:51 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 [this message]
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       ` [MODERATED] Re: [PATCH v4 04/10] TAAv4 4 Josh Poimboeuf
2019-09-26  0:48         ` 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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