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Date: Fri, 21 Oct 2022 20:05:39 +0200
From: Juergen Gross <jgross@...e.com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v4 03/16] x86/mtrr: replace use_intel() with a local flag
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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