[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v2 02/10] x86/mtrr: remove unused cyrix_set_all() function
On 25.08.22 12:31, Borislav Petkov wrote:
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...
Maybe the alternative reasoning is much faster to understand: if the
Cyrix set_all() could be called, the AMD and Centaur ones would be callable,
too. Those being called would result in a NULL deref, so why should we keep
the Cyrix one?
Juergen
Attachment:
OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature
|
