Re: [PATCH] UefiCpuPkg/MtrrLib: Add flag to skip disabling MTRRs prior to MTRR change.

["Duran, Leo" <leo.duran@amd.com>]

> -----Original Message-----
> From: Ni, Ruiyu [mailto:ruiyu.ni@Intel.com]
> Sent: Tuesday, September 18, 2018 3:34 AM
> To: Laszlo Ersek <lersek@redhat.com>; Duran, Leo <leo.duran@amd.com>;
> edk2-devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>
> Subject: Re: [edk2] [PATCH] UefiCpuPkg/MtrrLib: Add flag to skip disabling
> MTRRs prior to MTRR change.
> 
> On 9/18/2018 12:38 AM, Laszlo Ersek wrote:
> > On 09/17/18 18:20, Duran, Leo wrote:
> >>
> >>> -----Original Message-----
> >>> From: Ni, Ruiyu <ruiyu.ni@Intel.com>
> >>> Sent: Thursday, September 13, 2018 11:44 PM
> >>> To: Duran, Leo <leo.duran@amd.com>; Laszlo Ersek
> >>> <lersek@redhat.com>; edk2-devel@lists.01.org
> >>> Cc: Dong, Eric <eric.dong@intel.com>
> >>> Subject: Re: [edk2] [PATCH] UefiCpuPkg/MtrrLib: Add flag to skip
> >>> disabling MTRRs prior to MTRR change.
> >>>
> >>> On 9/14/2018 3:31 AM, Duran, Leo wrote:
> >>>>
> >>>>
> >>>>> -----Original Message-----
> >>>>> From: Ni, Ruiyu <ruiyu.ni@intel.com>
> >>>>> Sent: Wednesday, September 12, 2018 9:39 PM
> >>>>> To: Duran, Leo <leo.duran@amd.com>; Laszlo Ersek
> >>> <lersek@redhat.com>;
> >>>>> edk2-devel@lists.01.org
> >>>>> Cc: Dong, Eric <eric.dong@intel.com>
> >>>>> Subject: RE: [PATCH] UefiCpuPkg/MtrrLib: Add flag to skip
> >>>>> disabling MTRRs prior to MTRR change.
> >>>>>
> >>>>> Leo,
> >>>>> Sorry I was in leave yesterday so didn't see the mail.
> >>>>> Which MSRs are shared? Only the
> >>> MSR_IA32_MTRR_DEF_TYPE_REGISTER?
> >>>>> Or all the MSRs that configures the CPU MTRR setting?
> >>>>>
> >>>>
> >>>> Hi Ray,
> >>>> The MTTR config MSRs are also shared by threads within a core.
> >>>>
> >>>
> >>> Hi Leo,
> >>> Do you think that fixing the caller is more proper?
> >>
> >> Hi Ray,
> >> Actually,
> >> The proposed PCD is the simplest solution, as that works for us and does
> not change the existing (default) flow.
> >>
> >> That is,
> >> I'd prefer making a decision about the PCD in platform-specific code,
> rather than introducing complex detection and heuristics at the caller level in
> EDK2 (just for AMD).
> >>
> >> So, please approve the PCD.
> 
> Leo,
> I agree with you on the first part "the PCD is the simplest solution".
> But this really looks like a workaround of the real issue.
> For a multiple-socket system, it may contain S sockets, each socket contains C
> cores and each core contains T threads. In summary the system contains S *
> C * T threads.
> As you said all threads inside a core share the MTRR setting.
> Do all cores inside a socket share the MTRR setting?
> Do all sockets share the MTRR setting?
> 
> If one of the answer of above questions is "no", how can we configure the
> PCD?
> 
[Duran, Leo] 
Hi Ray,
The MTTR settings are share by threads within a core (but each core has its own, etc.)
The PCD would be set in our platform-specific code (e.g., it can be set at build-time in the .DSC file).

As I mentioned, 
We don't need (Mtrr.Enable=0) to change MTRR settings, so having the PCD to skip (Mtrr.Enable=0) is reasonable for us.

Leo.

> >
> > - From my side, if it works for you, it works for me. (The general
> > trend has been to avoid adding more PCDs to the "core" package DEC
> > files, but I'm 100% neutral on that.)
> >
> > Laszlo
> >
> 
> Laszlo,
> Thanks for pointing out the general trend. Yes less PCDs are very welcomed.
> To me, PCD is no different from protocol. And even worse, because it's very
> easily to be over-used.
> But I am not sure whether a PCD has to be introduced for this issue.
> Maybe even we choose to fix the caller, the PCD is still needed. I am not
> sure.
> 
> --
> Thanks,
> Ray