Re: [PATCH v4 03/16] x86/mtrr: replace use_intel() with a local flag

From: Juergen Gross
Date: Fri Oct 21 2022 - 14:05:53 EST


On 21.10.22 19:19, Borislav Petkov wrote:
On Tue, Oct 04, 2022 at 10:10:10AM +0200, Juergen Gross wrote:
In MTRR code use_intel() is only used in one source file, and the
relevant use_intel_if member of struct mtrr_ops is set only in
generic_mtrr_ops.

Replace use_intel() with a single flag in cacheinfo.c, which can be set
when assigning generic_mtrr_ops to mtrr_if. This allows to drop
use_intel_if from mtrr_ops, while preparing to support PAT without
MTRR. As another preparation for the PAT/MTRR decoupling use a bit for
MTRR control and one for PAT control. For now set both bits together,
this can be changed later.

As the new flag will be set only if mtrr_enabled is set, the test for
mtrr_enabled can be dropped at some places.

At the same time drop the local mtrr_enabled() function and rename
the __mtrr_enabled flag to mtrr_enabled.

So, I kinda like your idea about "replace the bool with mtrr_if != NULL"
to test whether MTRRs are enabled.

IOW, how does this look ontop of yours?

At the end of mtrr_bp_init() I need to do some careful dancing but I
think this way it is even clearer. I'm pretty sure it can be simplified
even more but one thing at a time...

Please have a look at patch 10 (I've put it after the rework of mtrr_bp_init()
exactly in order to avoid the dance you had to do).


Juergen


Thx.

---
diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
index dacb537da126..927b463a22bd 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.c
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
@@ -59,7 +59,6 @@
#define MTRR_TO_PHYS_WC_OFFSET 1000
u32 num_var_ranges;
-static bool mtrr_enabled;
unsigned int mtrr_usage_table[MTRR_MAX_VAR_RANGES];
static DEFINE_MUTEX(mtrr_mutex);
@@ -71,15 +70,17 @@ static const struct mtrr_ops *mtrr_ops[X86_VENDOR_NUM] __ro_after_init;
const struct mtrr_ops *mtrr_if;
-static void set_mtrr(unsigned int reg, unsigned long base,
- unsigned long size, mtrr_type type);
-
void __init set_mtrr_ops(const struct mtrr_ops *ops)
{
if (ops->vendor && ops->vendor < X86_VENDOR_NUM)
mtrr_ops[ops->vendor] = ops;
}
+static bool mtrr_enabled(void)
+{
+ return !!mtrr_if;
+}
+
/* Returns non-zero if we have the write-combining memory type */
static int have_wrcomb(void)
{
@@ -299,7 +300,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
int i, replace, error;
mtrr_type ltype;
- if (!mtrr_enabled)
+ if (!mtrr_enabled())
return -ENXIO;
error = mtrr_if->validate_add_page(base, size, type);
@@ -447,7 +448,7 @@ static int mtrr_check(unsigned long base, unsigned long size)
int mtrr_add(unsigned long base, unsigned long size, unsigned int type,
bool increment)
{
- if (!mtrr_enabled)
+ if (!mtrr_enabled())
return -ENODEV;
if (mtrr_check(base, size))
return -EINVAL;
@@ -476,7 +477,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
unsigned long lbase, lsize;
int error = -EINVAL;
- if (!mtrr_enabled)
+ if (!mtrr_enabled())
return -ENODEV;
max = num_var_ranges;
@@ -536,7 +537,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
*/
int mtrr_del(int reg, unsigned long base, unsigned long size)
{
- if (!mtrr_enabled)
+ if (!mtrr_enabled())
return -ENODEV;
if (mtrr_check(base, size))
return -EINVAL;
@@ -562,7 +563,7 @@ int arch_phys_wc_add(unsigned long base, unsigned long size)
{
int ret;
- if (pat_enabled() || !mtrr_enabled)
+ if (pat_enabled() || !mtrr_enabled())
return 0; /* Success! (We don't need to do anything.) */
ret = mtrr_add(base, size, MTRR_TYPE_WRCOMB, true);
@@ -750,15 +751,18 @@ void __init mtrr_bp_init(void)
}
}
- if (mtrr_if) {
- mtrr_enabled = true;
- set_num_var_ranges(mtrr_if == &generic_mtrr_ops);
+ if (mtrr_enabled()) {
+ bool use_generic = mtrr_if == &generic_mtrr_ops;
+ bool mtrr_state_enabled = true;
+
+ set_num_var_ranges(use_generic);
init_table();
- if (mtrr_if == &generic_mtrr_ops) {
+
+ if (use_generic) {
/* BIOS may override */
- mtrr_enabled = get_mtrr_state();
+ mtrr_state_enabled = get_mtrr_state();
- if (mtrr_enabled) {
+ if (mtrr_state_enabled) {
mtrr_bp_pat_init();
memory_caching_control |= CACHE_MTRR | CACHE_PAT;
}
@@ -767,10 +771,13 @@ void __init mtrr_bp_init(void)
changed_by_mtrr_cleanup = 1;
mtrr_if->set_all();
}
+
+ if (!mtrr_state_enabled)
+ mtrr_if = NULL;
}
}
- if (!mtrr_enabled) {
+ if (!mtrr_enabled()) {
pr_info("Disabled\n");
/*
@@ -811,7 +818,7 @@ void mtrr_save_state(void)
{
int first_cpu;
- if (!mtrr_enabled)
+ if (!mtrr_enabled())
return;
first_cpu = cpumask_first(cpu_online_mask);
@@ -856,7 +863,7 @@ void mtrr_bp_restore(void)
static int __init mtrr_init_finialize(void)
{
- if (!mtrr_enabled)
+ if (!mtrr_enabled())
return 0;
if (memory_caching_control & CACHE_MTRR) {


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