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

[Juergen Gross]

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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