Re: [tip:x86/urgent] x86, cpu, amd: Add workaround for family 16h, erratum 793

Ingo Molnar
2014-01-15T06:28:23Z

* H. Peter Anvin <hpa@zytor.com> wrote:

> On 01/14/2014 04:45 PM, tip-bot for Borislav Petkov wrote:
> > + rdmsrl(MSR_AMD64_LS_CFG, val);
> > + if (!(val & BIT(15)))
> > + wrmsrl(MSR_AMD64_LS_CFG, val | BIT(15));
>
> Incidentally, I'm wondering if we shouldn't have a
> set_in_msr()/clear_in_msr() set of functions which would incorporate the
> above construct:
>
> void set_in_msr(u32 msr, u64 mask)
> {
> u64 old, new;
>
> old = rdmsrl(msr);
> new = old | mask;
> if (old != new)
> wrmsrl(msr, new);
> }
>
> ... and the obvious equivalent for clear_in_msr().
>
> The perhaps only question is if it should be "set/clear_bit_in_msr()"
> rather than having to haul a full 64-bit mask in the common case.

I'd suggest the introduction of a standard set of methods operating on
MSRs:

msr_read()
msr_write()
msr_set_bit()
msr_clear_bit()
msr_set_mask()
msr_clear_mask()

etc.

msr_read() would essentially map to rdmsr_safe(). Each method has a
return value that can be checked for failure.

Note that the naming of 'msr_set_bit()' and 'msr_clear_bit()' mirrors
that of bitops, and set_mask/clear_mask is named along a similar
pattern, so that it's more immediately obvious what's going on.

With such methods in place we could use them in most new code, and
would use 'raw, unsafe' rdmsr()/wrmsr() only in very specific,
justified cases.

Thanks,

Ingo