Re: [Xen-devel] [PATCH v11 13/23] x86: refactor psr: CDP: implement CPU init flow.

[Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx>]

On 17-06-07 09:31:02, Yi Sun wrote:
> On 17-06-06 02:38:27, Jan Beulich wrote:
> > >>> On 06.06.17 at 10:13, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> > > On 17-06-06 01:45:11, Jan Beulich wrote:
> > >> >>> On 02.06.17 at 09:26, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> > >> > On 17-05-31 03:37:48, Jan Beulich wrote:
> > >> >> >>> On 03.05.17 at 10:44, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> > >> >> > +        /* Cut half of cos_max when CDP is enabled. */
> > >> >> > +        feat->cos_max >>= 1;
> > >> >> > +
> > >> >> > +        /* We only write mask1 since mask0 is always all ones by 
> > >> >> > default. */
> > >> >> 
> > >> >> Is this, btw, just reset state or even guaranteed after offlining
> > >> >> and re-onlining a CPU?
> > >> >> 
> > >> > Below MSRs are all per socket. So, we just need reset them when socket 
> > >> > is
> > >> > online.
> > >> 
> > >> Which I hope you've understood then means the comment and
> > >> presumably also the code here need further refinement.
> > >> 
> > > Spec states it below. So, the mask0 is guranteed.
> > > "the default mask in IA32_L3_MASK_0 - which is all “1”s (on reset)"
> > 
> > Sigh. I did ask very clearly (and this is still visible above) about
> > the case where the CPU did _not_ undergo a reset cycle.
> > 
> Sorry, I think I must mis-understand your question. SW never modifies value
> of COS ID 0 mask register. So, the value in mask0 will not be changed after
> socket first online (mask0 is set to default by HW this time). So, we think
> it is not necessary to restore mask0 value to default here.
> 
But considering something else (e.g. FW) may change this MSR value during
socket offline-online cycle, we may need to restore mask0 here too. Is that
your intention? Thanks!

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