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 1/6] x86/mm/pat: Change PAT to support non-default PAT MSR
Date: Tue, 22 Mar 2016 17:57:26 +0100 [thread overview]
Message-ID: <20160322165725.GB5656__35687.4044322923$1458665937$gmane$org@pd.tnic> (raw)
In-Reply-To: <1458175502-31936-2-git-send-email-toshi.kani@hpe.com>
$Subject is misleading - there's no non-default PAT MSR - the setting is
non-default.
On Wed, Mar 16, 2016 at 06:44:57PM -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
> support a case that PAT MSR is initialized with a non-default
> value.
>
> When pat_init() is called in PAT disable state, it initializes
is called and PAT is disabled
> PAT table with the BIOS default value. Xen, however, sets PAT MSR
> with a non-default value to enable WC. This causes inconsistency
> between PAT table and PAT MSR when PAT is set to disable on Xen.
>
> Change pat_init() to handle the PAT disable cases properly. Add
> pat_keep_handoff_state() to handle two cases when PAT is set to
> disable.
> 1. CPU supports PAT: Set PAT table to be consistent with PAT MSR.
> 2. CPU does not support PAT: Set PAT table to be consistent with
> PWT and PCD bits in a PTE.
>
> 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: Ingo Molnar <mingo@kernel.org>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/mm/pat.c | 80 +++++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 62 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 04e2e71..e0a34b0 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -207,9 +207,6 @@ static void pat_bsp_init(u64 pat)
> return;
> }
>
> - if (!pat_enabled())
> - goto done;
> -
> rdmsrl(MSR_IA32_CR_PAT, tmp_pat);
> if (!tmp_pat) {
> pat_disable("PAT MSR is 0, disabled.");
> @@ -218,15 +215,11 @@ static void pat_bsp_init(u64 pat)
>
> wrmsrl(MSR_IA32_CR_PAT, pat);
>
> -done:
> pat_init_cache_modes(pat);
> }
>
> static void pat_ap_init(u64 pat)
> {
> - if (!pat_enabled())
> - return;
> -
> if (!cpu_has_pat) {
> /*
> * If this happens we are on a secondary CPU, but switched to
> @@ -238,18 +231,43 @@ static void pat_ap_init(u64 pat)
> wrmsrl(MSR_IA32_CR_PAT, pat);
> }
>
> -void pat_init(void)
> +/**
> + * pat_keep_handoff_state - Set PAT table to the handoff state
> + *
> + * This function keeps PAT in the BIOS handoff state. When CPU supports
> + * PAT, it sets PAT table to be consistent with PAT MSR. When CPU does not
> + * support PAT, it emulates PAT by setting PAT table consistent with PWT
> + * and PCD bits in a PTE.
> + *
> + * The PAT table is global to all CPUs, which is initialized once at
> + * boot-time. Any subsequent calls to this function have no effect.
> + */
> +static void pat_keep_handoff_state(void)
Static function, no need for "pat_" prefix. Also, no need for the
kernel-doc comment.
Also, no need for all that handoff nomenclature etc, just call it
setup_pat(). Because it does exactly that - it sets up the PAT bits
unconditionally, regardless of enabled or not.
> {
> - u64 pat;
> - struct cpuinfo_x86 *c = &boot_cpu_data;
> + u64 pat = 0;
> + static int set_handoff_done;
s/set_handoff_done/pat_setup_done/
--
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 16:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1458175502-31936-1-git-send-email-toshi.kani@hpe.com>
2016-03-17 0:44 ` [PATCH v2 1/6] x86/mm/pat: Change PAT to support non-default PAT MSR Toshi Kani
[not found] ` <1458175502-31936-2-git-send-email-toshi.kani@hpe.com>
2016-03-22 16:57 ` Borislav Petkov [this message]
[not found] ` <20160322165725.GB5656@pd.tnic>
2016-03-22 18:35 ` Toshi Kani
2016-03-23 8:43 ` Borislav Petkov
2016-03-23 15:46 ` Toshi Kani
2016-03-22 19:17 ` Thomas Gleixner
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