Re: [PATCH v3 03/10] x86/mtrr: replace use_intel() with a local flag

From: Juergen Gross
Date: Mon Sep 12 2022 - 05:10:36 EST


On 11.09.22 12:16, Borislav Petkov wrote:
On Thu, Sep 08, 2022 at 10:49:07AM +0200, Juergen Gross wrote:
diff --git a/arch/x86/include/asm/cacheinfo.h b/arch/x86/include/asm/cacheinfo.h
index 86b2e0dcc4bf..1aeafa9888f7 100644
--- a/arch/x86/include/asm/cacheinfo.h
+++ b/arch/x86/include/asm/cacheinfo.h
@@ -2,6 +2,11 @@
#ifndef _ASM_X86_CACHEINFO_H
#define _ASM_X86_CACHEINFO_H
+/* Kernel controls MTRR and/or PAT MSRs. */
+extern unsigned int cache_generic;

So this should be called something more descriptive like

memory_caching_types

In the end this variable doesn't specify which caching types are available,
but the ways to select/control the caching types.

So what about "memory_caching_select" or "memory_caching_control" instead?

or so to denote that this is a bitfield of supported memory caching
technologies. The code then would read as

if (memory_caching_types & CACHE_MTRR)

The name's still not optimal tho - needs more brooding over.

+#define CACHE_GENERIC_MTRR 0x01
+#define CACHE_GENERIC_PAT 0x02

And those should be CACHE_{MTRR,PAT}.

Fine with me.

void cacheinfo_amd_init_llc_id(struct cpuinfo_x86 *c, int cpu);
void cacheinfo_hygon_init_llc_id(struct cpuinfo_x86 *c, int cpu);
diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index 66556833d7af..3b05d3ade7a6 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -35,6 +35,9 @@ DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
/* Shared L2 cache maps */
DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_l2c_shared_map);
+/* Kernel controls MTRR and/or PAT MSRs. */
+unsigned int cache_generic;

This should either be __ro_after_init and initialized to 0 or you need
accessors...

Okay.


u32 num_var_ranges;
-static bool __mtrr_enabled;
-
-static bool mtrr_enabled(void)
-{
- return __mtrr_enabled;
-}
+static bool mtrr_enabled;

Hmm, I don't like this. There's way too many boolean flags in the mtrr
code. There's mtrr_state.enabled too. ;-\

Can we set (or clear) X86_FEATURE_MTRR to denote MTRR enablement status
and get rid of one more boolean flag?

I'll have a look.


...

void __init mtrr_bp_init(void)
{
+ bool use_generic = false;
u32 phys_addr;
init_ifs();
@@ -694,6 +691,7 @@ void __init mtrr_bp_init(void)
if (boot_cpu_has(X86_FEATURE_MTRR)) {
mtrr_if = &generic_mtrr_ops;
+ use_generic = true;
size_or_mask = SIZE_OR_MASK_BITS(36);
size_and_mask = 0x00f00000;
phys_addr = 36;
@@ -755,15 +753,18 @@ void __init mtrr_bp_init(void)
}
if (mtrr_if) {
- __mtrr_enabled = true;
- set_num_var_ranges();
+ mtrr_enabled = true;
+ set_num_var_ranges(use_generic);

You don't need use_generic either:

set_num_var_ranges(mtrr_if == generic_mtrr_ops);

(The reason being I wanna get rid of that nasty minefield of boolean
vars all round that code).

Fine with me.


Juergen

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