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

[Juergen Gross]

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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