linux-kernel - Re: [PATCH] KVM: nVMX: Remove outdated comments in nested_vmx_setup_ctls

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Date:   Mon, 19 Dec 2022 17:53:07 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     pbonzini@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Remove outdated comments in
 nested_vmx_setup_ctls_msrs().

On Fri, Dec 16, 2022 at 04:49:55PM +0000, Sean Christopherson wrote:
> On Fri, Dec 16, 2022, Yu Zhang wrote:
> > > 
> > > Eh, just drop the comment.  Pretty obvious this is for secondary execution controls.
> > Thanks Sean. Well, I agree it is obvious.
> > 
> > This line was kept because there are comments for other groups of
> > control fields(e.g., exit/entry/pin-based/cpu-based controls etc.)
> > in nested_vmx_setup_ctls_msrs(). If we do not keep the one for secondary
> > cpu-based controls, we may just delete other comments as well. But
> > is that really necessary? 
> 
> Adding a patch to delete the various one-line comments is probably unnecessary
> churn.  The comments are kinda sorta helpful, but only because the function is a
> giant and thus a bit hard to follow.  A better solution than comments would be to
> add helpers for each collection ("secondary_ctls" is a bit of a lie because it
> handle VPID, EPT, VMFUNC, etc..., but whatever), e.g.

Good point. The "secondary_ctls" may be inaccurate, but I do not
have a better name in mind either...

> 
> 	nested_vmx_setup_pinbased_ctls(msrs);
> 	nested_vmx_setup_exit_ctls(msrs);
> 	nested_vmx_setup_entry_ctls(msrs);
> 	nested_vmx_setup_cpubased_ctls(msrs);
> 	nested_vmx_setup_secondary_ctls(msrs);
Adding nested_vmx_setup_secondary_ctls() will impact
1> your previous patch to expose ENABLE_USR_WAIT_PAUSE control
https://lore.kernel.org/lkml/20221213062306.667649-2-seanjc@google.com/
2> my previous patch to simplify the setting of secondary proc-
based control:
https://www.spinics.net/lists/kernel/msg4582141.html
How about we combine our previous patches and the new ones together
in next version?

One more questionable comment for nested_vmx_setup_ctls_msrs() is:

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index b6f4411b613e..58b491f13ed7 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6744,8 +6744,6 @@ static u64 nested_vmx_calc_vmcs_enum_msr(void)
 /*
  * nested_vmx_setup_ctls_msrs() sets up variables containing the values to be
  * returned for the various VMX controls MSRs when nested VMX is enabled.
- * The same values should also be used to verify that vmcs12 control fields are
- * valid during nested entry from L1 to L2.
  * Each of these control msrs has a low and high 32-bit half: A low bit is on
  * if the corresponding bit in the (32-bit) control field *must* be on, and a
  * bit in the high half is on if the corresponding bit in the control field


> 	nested_vmx_setup_misc_data(msrs);
As to the misc data msr, do we really need a seperate function for it?
If yes, then what about the vmx basic msr, the ones for fixed bits in
CR0/4? 

B.R.
Yu