Re: [PATCH 2/2] x86/vmx: implement Notify VM Exit

From: Jan Beulich <jbeulich@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Kevin Tian <kevin.tian@intel.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH 2/2] x86/vmx: implement Notify VM Exit
Date: Thu, 19 May 2022 16:14:46 +0200	[thread overview]
Message-ID: <90c4d10e-1304-822d-ff85-9f86561d5b00@suse.com> (raw)
In-Reply-To: <YoY7lrpnSMJjmurA@Air-de-Roger>

On 19.05.2022 14:44, Roger Pau Monné wrote:
> On Thu, May 19, 2022 at 08:50:55AM +0200, Jan Beulich wrote:
>> On 17.05.2022 15:21, Roger Pau Monne wrote:
>>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>>> @@ -4567,6 +4567,30 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
>>>           */
>>>          break;
>>>  
>>> +    case EXIT_REASON_NOTIFY:
>>> +        __vmread(EXIT_QUALIFICATION, &exit_qualification);
>>> +
>>> +        if ( exit_qualification & NOTIFY_VM_CONTEXT_INVALID )
>>> +        {
>>> +            perfc_incr(vmnotify_crash);
>>
>> Is this a useful event to count? We don't count other crash causes,
>> iirc.
> 
> I thought it was helpful information from an admin PoV, but maybe I'm
> mistaken.  I know we don't count other crash reasons, but that doesn't
> mean it won't be helpful to do so.  Given that users have to opt-in to
> enable counters I suggest to leave the counter there.

Just to be explicit: I don't mind the counter, I merely find its addition
inconsistent with what we've got.

Jan