From: Borislav Petkov <bp@alien8.de>
To: Juergen Gross <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2 02/10] x86/mtrr: remove unused cyrix_set_all() function
Date: Thu, 25 Aug 2022 12:31:11 +0200 [thread overview]
Message-ID: <YwdPb4pWqppgzIpm@zn.tnic> (raw)
In-Reply-To: <20220820092533.29420-3-jgross@suse.com>
On Sat, Aug 20, 2022 at 11:25:25AM +0200, Juergen Gross wrote:
> The Cyrix cpu specific MTRR function cyrix_set_all() will never be
> called, as the struct mtrr_ops set_all() callback will only be called
> in the use_intel() case, which would require the use_intel_if member
> of struct mtrr_ops to be set, which isn't the case for Cyrix.
Doing some git archeology:
So the commit which added mtrr_aps_delayed_init is
d0af9eed5aa9 ("x86, pat/mtrr: Rendezvous all the cpus for MTRR/PAT init")
from 2009.
The IPI callback before it, looked like this:
static void ipi_handler(void *info)
{
#ifdef CONFIG_SMP
struct set_mtrr_data *data = info;
unsigned long flags;
local_irq_save(flags);
atomic_dec(&data->count);
while (!atomic_read(&data->gate))
cpu_relax();
/* The master has cleared me to execute */
if (data->smp_reg != ~0U) {
mtrr_if->set(data->smp_reg, data->smp_base,
data->smp_size, data->smp_type);
} else {
mtrr_if->set_all();
^^^^^^^^^
and that else branch would call ->set_all() on Cyrix too.
Suresh's patch changed it to do:
- } else {
+ } else if (mtrr_aps_delayed_init) {
+ /*
+ * Initialize the MTRRs inaddition to the synchronisation.
+ */
mtrr_if->set_all();
BUT below in the set_mtrr() call, it did:
/*
* HACK!
* We use this same function to initialize the mtrrs on boot.
* The state of the boot cpu's mtrrs has been saved, and we want
* to replicate across all the APs.
* If we're doing that @reg is set to something special...
*/
if (reg != ~0U)
mtrr_if->set(reg, base, size, type);
else if (!mtrr_aps_delayed_init)
mtrr_if->set_all();
^^^
and that would be the Cyrix case.
But then
192d8857427d ("x86, mtrr: use stop_machine APIs for doing MTRR rendezvous")
came and "cleaned" all up by removing the "HACK" and doing ->set_all()
only in the rendezvous handler:
+ } else if (mtrr_aps_delayed_init || !cpu_online(smp_processor_id())) {
mtrr_if->set_all();
}
Which begs the question: why doesn't the second part of the else test
match on Cyrix? The "|| !cpu_online(smp_processor_id())" case.
If only we had a Cyrix machine somewhere...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2022-08-25 10:31 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-20 9:25 [PATCH v2 00/10] x86: make pat and mtrr independent from each other Juergen Gross
2022-08-20 9:25 ` [PATCH v2 01/10] x86/mtrr: fix MTRR fixup on APs Juergen Gross
2022-08-20 10:28 ` Greg KH
2022-08-21 12:25 ` Borislav Petkov
2022-08-21 21:41 ` Borislav Petkov
2022-08-22 5:17 ` Juergen Gross
2022-08-22 8:28 ` Borislav Petkov
2022-08-22 8:32 ` Juergen Gross
2022-10-19 18:45 ` [tip: x86/cpu] x86/mtrr: Add comment for set_mtrr_state() serialization tip-bot2 for Juergen Gross
2022-08-20 9:25 ` [PATCH v2 02/10] x86/mtrr: remove unused cyrix_set_all() function Juergen Gross
2022-08-25 10:31 ` Borislav Petkov [this message]
2022-08-25 10:38 ` Juergen Gross
2022-08-25 10:41 ` Juergen Gross
2022-08-25 11:42 ` Borislav Petkov
2022-08-25 12:13 ` Juergen Gross
2022-08-20 9:25 ` [PATCH v2 03/10] x86/mtrr: replace use_intel() with a local flag Juergen Gross
2022-08-20 9:25 ` [PATCH v2 04/10] x86: move some code out of arch/x86/kernel/cpu/mtrr Juergen Gross
2022-08-20 9:25 ` [PATCH v2 05/10] x86/mtrr: split generic_set_all() Juergen Gross
2022-08-20 9:25 ` [PATCH v2 06/10] x86/mtrr: remove set_all callback from struct mtrr_ops Juergen Gross
2022-08-20 9:25 ` [PATCH v2 07/10] x86/mtrr: simplify mtrr_bp_init() Juergen Gross
2022-08-20 9:25 ` [PATCH v2 08/10] x86/mtrr: let cache_aps_delayed_init replace mtrr_aps_delayed_init Juergen Gross
2022-08-20 9:25 ` [PATCH v2 09/10] x86/mtrr: add a stop_machine() handler calling only cache_cpu_init() Juergen Gross
2022-08-20 9:25 ` [PATCH v2 10/10] x86: decouple pat and mtrr handling Juergen Gross
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