Re: [PATCH 05/32] x86/mtrr: Stop using 32-bit MSR interfaces

[Jürgen Groß]

On 29.06.26 13:33, Ingo Molnar wrote:
> * Juergen Gross <jgross@xxxxxxxx> wrote:
>
> >   amd_get_mtrr(unsigned int reg, unsigned long *base,
> >   	     unsigned long *size, mtrr_type *type)
> >   {
> > -	unsigned long low, high;
> > +	unsigned long val;
> > +	struct msr msr;
>
> So, 'struct msr' is defined in <asm/msr.h>, but:
>
> >   static void
> >   amd_set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type type)
> >   {
> > -	u32 regs[2];
> > +	union {
> > +		u32 regs[2];
> > +		u64 val;
> > +	} msr;
>
> Why do we use a local anonymous union here with overlapping
> nomenclature and a confusingly different but (AFAICS) functionally
> equivalent definition to 'struct msr'?

This is done in order to avoid having to change the code too much. As an
alternative I could use struct msr by doing:

  rdmsrq(MSR_K6_UWCCR, msr.q);
  regs[0] = msr.l;
  regs[1] = msr.h;

  ...

  msr.l = regs[0];
  msr.h = regs[1];
  wrmsrq(MSR_K6_UWCCR, msr.q);


Juergen

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