From: Toshi Kani <toshi.kani@hpe.com>
To: Borislav Petkov <bp@suse.de>
Cc: jgross@suse.com, mcgrof@suse.com, x86@kernel.org,
linux-kernel@vger.kernel.org, paul.gortmaker@windriver.com,
hpa@zytor.com, xen-devel@lists.xenproject.org,
tglx@linutronix.de, mingo@kernel.org, elliott@hpe.com
Subject: Re: [PATCH v2 2/6] x86/mm/pat: Add pat_disable() interface
Date: Tue, 22 Mar 2016 15:40:45 -0600 [thread overview]
Message-ID: <1458682845.6393.614.camel__21180.3231308751$1458679776$gmane$org@hpe.com> (raw)
In-Reply-To: <20160322165944.GC5656@pd.tnic>
On Tue, 2016-03-22 at 17:59 +0100, Borislav Petkov wrote:
> On Wed, Mar 16, 2016 at 06:46:55PM -0600, Toshi Kani wrote:
> > In preparation to fix a regression caused by 'commit 9cd25aac1f44
> > ("x86/mm/pat: Emulate PAT when it is disabled")', PAT needs to
> > provide an interface that disables the OS to initialize PAT MSR.
>
> prevents the OS from initializing the PAT MSR.
Right. Will do.
> >
> > PAT MSR initialization must be done on all CPUs with the specific
>
> s/with/using/
Ditto.
> > sequence of operations defined in Intel SDM. This requires MTRR
> ^
> the
>
> s/MTRR/MTRRs/
Ditto.
> > to be enabled since pat_init() is called as part of MTRR init
> > from mtrr_rendezvous_handler().
> >
> > Change pat_disable() as the interface to disable the OS to initialize
> > PAT MSR, and set PAT table with pat_keep_handoff_state(). This
> > interface can be called when PAT initialization may not be performed.
>
> This paragraph reads funky and I can't really parse what it is trying to
> say.
Sorry... Here is a retry:
Make pat_disable() as the interface that prevents the OS from initializing
the PAT MSR. MTRR will call this interface when it cannot provide the SDM-
defined sequence to initialize PAT.
> > This also assures that pat_disable() called from pat_bsp_init()
> > to set PAT table properly when CPU does not support PAT.
> >
:
> >
> > -static inline void pat_disable(const char *reason)
> > +/**
> > + * pat_disable() - Disable the OS to initialize PAT MSR
>
> ^^^^
>
> Err, what? The function name can't be more clear.
Will change to "Prevent the OS from initializing the PAT MSR".
I wanted to clarify that "disable" does not mean to disable PAT MSR.
> > + *
> > + * This function disables the OS to initialize PAT MSR, and calls
>
> "prevents the OS from initializing the PAT MSR..."
Will do.
> > + * pat_keep_handoff_state() to set PAT table to the handoff state.
>
> We can see what is calls. You're explaining *what* the code does instead
> of *why* again.
Right...
> > + */
> > +void pat_disable(const char *reason)
> > {
>
> Why aren't you checking __pat_enabled here?
>
> if (!__pat_enabled)
> return;
pat_keep_handoff_state() is a no-op after the initial call, but I agree
that having this check is better. Will do.
> You can save yourself the other guards in that function, especially that
> pr_err() below.
The pr_err() below is for a difference case -- PAT is enabled, but a call
is made to disable it after pat_init() is called. We cannot allow this
case.
> > + if (boot_cpu_done) {
> > + pr_err("x86/PAT: PAT cannot be disabled after
> > initialization "
> > + "(attempting: %s)\n", reason);
>
> Please integrate checkpatch.pl into your patch creation workflow as it
> sometimes has valid complaints:
>
> WARNING: quoted string split across lines
> #79: FILE: arch/x86/mm/pat.c:55:
> + pr_err("x86/PAT: PAT cannot be disabled after
> initialization "
> + "(attempting: %s)\n", reason);
I've run checkpatch.pl and thought it was OK to have this warning (instead
of a >80 warning) since the error message part was not split. The
"attempting" part is for debugging and its string is passed from the
caller.
> More to the point: why do we need that pr_err() call? What is that
> supposed to tell the user?
>
> I think it is more for the programmer to catch wrong use of
> pat_disable() and then it should be WARN_ONCE() or so...
Yes, this case is for the programmer to catch wrong use. I will change it
to use WARN_ONCE() and remove the "(attempting: %s)\n" part of the message.
> > + return;
> > + }
> > +
> > __pat_enabled = 0;
> > pr_info("x86/PAT: %s\n", reason);
> > +
> > + pat_keep_handoff_state();
> > }
> >
> > static int __init nopat(char *str)
> > @@ -202,7 +217,7 @@ static void pat_bsp_init(u64 pat)
> > {
> > u64 tmp_pat;
> >
> > - if (!cpu_has_pat) {
> > + if (!boot_cpu_has(X86_FEATURE_PAT)) {
> > pat_disable("PAT not supported by CPU.");
> > return;
> > }
> > @@ -220,7 +235,7 @@ static void pat_bsp_init(u64 pat)
> >
> > static void pat_ap_init(u64 pat)
> > {
> > - if (!cpu_has_pat) {
> > + if (!boot_cpu_has(X86_FEATURE_PAT)) {
> > /*
> > * If this happens we are on a secondary CPU, but
> > switched to
> > * PAT on the boot CPU. We have no way to undo PAT.
>
> Those last two hunks are unrelated changes and should be a separate
> patch.
Will do.
Thanks,
-Toshi
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next prev parent reply other threads:[~2016-03-22 20:48 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-17 0:46 [PATCH v2 2/6] x86/mm/pat: Add pat_disable() interface Toshi Kani
2016-03-17 0:46 ` [PATCH v2 3/6] x86/mtrr: Fix Xorg crashes in Qemu sessions Toshi Kani
2016-03-17 0:46 ` [PATCH v2 4/6] x86/mtrr: Fix PAT init handling when MTRR MSR is disabled Toshi Kani
2016-03-17 0:46 ` [PATCH v2 5/6] x86/xen, pat: Remove PAT table init code from Xen Toshi Kani
2016-03-17 0:46 ` [PATCH v2 6/6] x86/pat: Document PAT initializations Toshi Kani
2016-03-22 16:59 ` [PATCH v2 2/6] x86/mm/pat: Add pat_disable() interface Borislav Petkov
[not found] ` <1458175619-32206-2-git-send-email-toshi.kani@hpe.com>
2016-03-22 17:00 ` [PATCH v2 3/6] x86/mtrr: Fix Xorg crashes in Qemu sessions Borislav Petkov
[not found] ` <20160322170047.GD5656@pd.tnic>
2016-03-22 21:53 ` Toshi Kani
[not found] ` <1458683610.6393.624.camel@hpe.com>
2016-03-23 8:44 ` Borislav Petkov
[not found] ` <20160323084437.GB8031@pd.tnic>
2016-03-23 15:53 ` Toshi Kani
[not found] ` <1458748393.6393.653.camel@hpe.com>
2016-03-23 21:47 ` Toshi Kani
[not found] ` <1458175619-32206-3-git-send-email-toshi.kani@hpe.com>
2016-03-22 17:01 ` [PATCH v2 4/6] x86/mtrr: Fix PAT init handling when MTRR MSR is disabled Borislav Petkov
[not found] ` <20160322170135.GE5656@pd.tnic>
2016-03-22 22:02 ` Toshi Kani
[not found] ` <1458175619-32206-4-git-send-email-toshi.kani@hpe.com>
2016-03-22 17:02 ` [PATCH v2 5/6] x86/xen, pat: Remove PAT table init code from Xen Borislav Petkov
[not found] ` <20160322170206.GF5656@pd.tnic>
2016-03-23 6:08 ` Juergen Gross
[not found] ` <1458175619-32206-5-git-send-email-toshi.kani@hpe.com>
2016-03-22 17:02 ` [PATCH v2 6/6] x86/pat: Document PAT initializations Borislav Petkov
[not found] ` <20160322170222.GG5656@pd.tnic>
2016-03-22 22:15 ` Toshi Kani
[not found] ` <20160322165944.GC5656@pd.tnic>
2016-03-22 21:40 ` Toshi Kani [this message]
[not found] ` <1458682845.6393.614.camel@hpe.com>
2016-03-23 8:51 ` [PATCH v2 2/6] x86/mm/pat: Add pat_disable() interface Borislav Petkov
[not found] ` <20160323085141.GC8031@pd.tnic>
2016-03-23 15:49 ` Toshi Kani
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