Re: [RFC PATCH 1/3] kvm: x86: Rename KVM_DEBUGREG_RELOAD to KVM_DEBUGREG_NEED_RELOAD

From: Xiaoyao Li <xiaoyao.li@intel.com>
To: Peter Xu <peterx@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
	kvm@vger.kernel.org, Nadav Amit <namit@cs.technion.ac.il>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/3] kvm: x86: Rename KVM_DEBUGREG_RELOAD to KVM_DEBUGREG_NEED_RELOAD
Date: Tue, 28 Apr 2020 00:06:20 +0800	[thread overview]
Message-ID: <3cc6471b-13da-832f-18d8-6db840b5ac47@intel.com> (raw)
In-Reply-To: <20200427143732.GD48376@xz-x1>

On 4/27/2020 10:37 PM, Peter Xu wrote:
> On Sat, Apr 25, 2020 at 09:48:17AM +0200, Paolo Bonzini wrote:
>> On 24/04/20 22:21, Peter Xu wrote:
>>> But then shouldn't DIRTY be set as long as KVM_DEBUGREG_BP_ENABLED is set every
>>> time before vmenter?  Then it'll somehow go back to switch_db_regs, iiuc...
>>>
>>> IIUC RELOAD actually wants to say "reload only for this iteration", that's why
>>> it's cleared after each reload.  So maybe...  RELOAD_ONCE?
>>>
>>> (Btw, do we have debug regs tests somewhere no matter inside guest or with
>>>   KVM_SET_GUEST_DEBUG?)
>>
>> What about KVM_DEBUGREG_EFF_DB_DIRTY?
> 
> The problem is iiuc we always reload eff_db[] no matter which bit in
> switch_db_regs is set, so this may still not clearly identify this bit from the
> rest of the two bits...
> 
> Actually I think eff_db[] is a bit confusing here in that it can be either the
> host specified dbreg values or the guest specified depends on the dynamic value
> of KVM_GUESTDBG_USE_HW_BP.
> 
> I am thinking maybe it's clearer to have host_db[] and guest_db[], then only
> until vmenter do we load either of them by:

host_db[] is somewhat misleading, how about user_db[] (just like user_fpu)

>    if (KVM_GUESTDBG_USE_HW_BP)
>      load(host_db[]);
>    else
>      load(gueet_db[]);
> 
> Then each db[] will be very clear on what's the data is about.  And we don't
> need to check KVM_GUESTDBG_USE_HW_BP every time when accessing eff_db[].
>