Messages in this thread Patch in this message | | | Date | Tue, 22 Mar 2016 17:59:44 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v2 2/6] x86/mm/pat: Add pat_disable() interface |
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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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