From: Borislav Petkov <bp@suse.de>
To: Toshi Kani <toshi.kani@hpe.com>
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 17:59:44 +0100 [thread overview]
Message-ID: <20160322165944.GC5656__49173.8545745195$1458666060$gmane$org@pd.tnic> (raw)
In-Reply-To: <1458175619-32206-1-git-send-email-toshi.kani@hpe.com>
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.
>
> PAT MSR initialization must be done on all CPUs with the specific
s/with/using/
> sequence of operations defined in Intel SDM. This requires MTRR
^
the
s/MTRR/MTRRs/
> 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.
> This also assures that pat_disable() called from pat_bsp_init()
> to set PAT table properly when CPU does not support PAT.
>
> Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Luis R. Rodriguez <mcgrof@suse.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Robert Elliott <elliott@hpe.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/include/asm/pat.h | 1 +
> arch/x86/mm/pat.c | 21 ++++++++++++++++++---
> 2 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
> index ca6c228..016142b 100644
> --- a/arch/x86/include/asm/pat.h
> +++ b/arch/x86/include/asm/pat.h
> @@ -5,6 +5,7 @@
> #include <asm/pgtable_types.h>
>
> bool pat_enabled(void);
> +void pat_disable(const char *reason);
> extern void pat_init(void);
> void pat_init_cache_modes(u64);
>
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index e0a34b0..48d1619 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -40,11 +40,26 @@
> static bool boot_cpu_done;
>
> static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
> +static void pat_keep_handoff_state(void);
>
> -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.
> + *
> + * This function disables the OS to initialize PAT MSR, and calls
"prevents the OS from initializing the PAT MSR..."
> + * 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.
> + */
> +void pat_disable(const char *reason)
> {
Why aren't you checking __pat_enabled here?
if (!__pat_enabled)
return;
You can save yourself the other guards in that function, especially that
pr_err() below.
> + 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);
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...
> + 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.
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--
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next prev parent reply other threads:[~2016-03-22 16:59 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 ` Borislav Petkov [this message]
[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 ` [PATCH v2 2/6] x86/mm/pat: Add pat_disable() interface Toshi Kani
[not found] ` <1458682845.6393.614.camel@hpe.com>
2016-03-23 8:51 ` Borislav Petkov
[not found] ` <20160323085141.GC8031@pd.tnic>
2016-03-23 15:49 ` Toshi Kani
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