Re: [PATCH v6 10/25] KVM: x86: Add kvm_msr_{read,write}() helpers

[Yang, Weijiang]

On 11/3/2023 2:26 AM, Maxim Levitsky wrote:
> On Wed, 2023-11-01 at 12:32 -0700, Sean Christopherson wrote:
> > On Tue, Oct 31, 2023, Maxim Levitsky wrote:
> > > On Thu, 2023-09-14 at 02:33 -0400, Yang Weijiang wrote:
> > > > Wrap __kvm_{get,set}_msr() into two new helpers for KVM usage and use the
> > > > helpers to replace existing usage of the raw functions.
> > > > kvm_msr_{read,write}() are KVM-internal helpers, i.e. used when KVM needs
> > > > to get/set a MSR value for emulating CPU behavior.
> > > I am not sure if I like this patch or not. On one hand the code is cleaner
> > > this way, but on the other hand now it is easier to call kvm_msr_write() on
> > > behalf of the guest.
> > >
> > > For example we also have the 'kvm_set_msr()' which does actually set the msr
> > > on behalf of the guest.
> > >
> > > How about we call the new function kvm_msr_set_host() and rename
> > > kvm_set_msr() to kvm_msr_set_guest(), together with good comments explaning
> > > what they do?
> > LOL, just call me Nostradamus[*] ;-)
> >
> >   : > SSP save/load should go to enter_smm_save_state_64() and rsm_load_state_64(),
> >   : > where other fields of SMRAM are handled.
> >   :
> >   : +1.  The right way to get/set MSRs like this is to use __kvm_get_msr() and pass
> >   : %true for @host_initiated.  Though I would add a prep patch to provide wrappers
> >   : for __kvm_get_msr() and __kvm_set_msr().  Naming will be hard, but I think we
> >                                               ^^^^^^^^^^^^^^^^^^^
> >   : can use kvm_{read,write}_msr() to go along with the KVM-initiated register
> >   : accessors/mutators, e.g. kvm_register_read(), kvm_pdptr_write(), etc.
> >
> > [*] https://lore.kernel.org/all/ZM0YZgFsYWuBFOze@xxxxxxxxxx
> >
> > > Also functions like kvm_set_msr_ignored_check(), kvm_set_msr_with_filter() and such,
> > > IMHO have names that are not very user friendly.
> > I don't like the host/guest split because KVM always operates on guest values,
> > e.g. kvm_msr_set_host() in particular could get confusing.
> That makes sense.
>
> > IMO kvm_get_msr() and kvm_set_msr(), and to some extent the helpers you note below,
> > are the real problem.
> >
> > What if we rename kvm_{g,s}et_msr() to kvm_emulate_msr_{read,write}() to make it
> > more obvious that those are the "guest" helpers?  And do that as a prep patch in
> > this series (there aren't _that_ many users).
> Makes sense.

Then I'll modify related code and add the pre-patch in next version, thanks!

> > I'm also in favor of renaming the "inner" helpers, but I think we should tackle
> > those separately.separately
> OK.
>
> Best regards,
> 	Maxim Levitsky