From: Alexandru Stefan ISAILA <aisaila@bitdefender.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Wei Liu <wl@xen.org>,
"kevin.tian@intel.com" <kevin.tian@intel.com>,
"tamas@tklengyel.com" <tamas@tklengyel.com>,
"jun.nakajima@intel.com" <jun.nakajima@intel.com>,
"rcojocaru@bitdefender.com" <rcojocaru@bitdefender.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Tim Deegan <tim@xen.org>, PaulDurrant <Paul.Durrant@citrix.com>,
"suravee.suthikulpanit@amd.com" <suravee.suthikulpanit@amd.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
"brian.woods@amd.com" <brian.woods@amd.com>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v5] x86/emulate: Send vm_event from emulate
Date: Mon, 1 Jul 2019 15:36:10 +0000 [thread overview]
Message-ID: <e38967e1-1705-5a3f-9601-a9a4b68f3ead@bitdefender.com> (raw)
In-Reply-To: <3fa5932d-174c-9b57-3cb6-aab4eb6a5238@suse.com>
On 01.07.2019 17:55, Jan Beulich wrote:
> On 01.07.2019 16:45, Alexandru Stefan ISAILA wrote:
>> On 01.07.2019 16:13, Jan Beulich wrote:
>>>>>> On 04.06.19 at 13:49, <aisaila@bitdefender.com> wrote:
>>>> + if ( !send_event || !pfec )
>>>> + return false;
>>>
>>> I think I've said before that the !pfec part need an explanation (in
>>> a comment). Without such an explanation I'm inclined to say it
>>> should be deleted. If otoh this is simply mean to be a shortcut,
>>> then you should really just check the two bits you actually care
>>> about further down.
>>
>> The pfec check is done because I encountered pfec 0 in tests. It could
>> save some work if pfec == 0 when calling the function. Is there
>> a must in having this check removed? If so then it can be done. The
>> send_event will be checked before calling the function as you said.
>
> It's not a requirement for it to be removed, _if_ there's a good
> reason for it to be there. I don't, however, see how pfec=0 could
> be a problem - afaict it would return false a few lines further
> down in that case.
You are right, pfec=0 wold not be a problem and it will be caught in the
no violation if.
>
>>>> + if ( !req.u.mem_access.flags )
>>>> + return false; /* no violation */
>>>
>>> How is the "false" here (I think this is the one the description talks
>>> about) matching up with the various other ones in the function?
>>
>> There should be no event if there is no access violation. So in this
>> case the emulation is continued as expected.
>
> But this doesn't answer my question: You use "false" as return value
> to indicate different things. Only the one here means "no access
> violation".
Sorry about that, since this will remain the only return false apart
form the main one (return monitor_traps()), false = event was not sent
and true = event was sent.
I understand that you are asking about the scenario when there was a
violation and the event was not sent. Then I can issue a domain_crash()
as that is potentially a big issue.
I hope I got that correctly.
>
>>>> @@ -615,6 +669,13 @@ static void *hvmemul_map_linear_addr(
>>>>
>>>> if ( pfec & PFEC_write_access )
>>>> {
>>>> + if ( hvm_emulate_send_vm_event(addr, gfn, pfec,
>>>> + hvmemul_ctxt->send_event) )
>>>> + {
>>>> + err = ERR_PTR(~X86EMUL_RETRY);
>>>> + goto out;
>>>> + }
>>>
>>> How come this sits only on the write path?
>>
>> We are interested only for the write access on this path. This also
>> ensures that pfec is set.
>
> I'm sorry, but the event sending should not be tailored to what you
> need or want. Or if so (i.e. if agreed upon among the VM event
> maintainers) then this restriction should be clearly spelled out.
>
On the other hand, this can go outside the write path with no effect on
the functionality of this send_event feature.
I will move it after the if(write) in the next version.
Thanks,
Alex
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next prev parent reply other threads:[~2019-07-01 15:36 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-01 13:13 [Xen-devel] [PATCH v5] x86/emulate: Send vm_event from emulate Jan Beulich
2019-07-01 14:45 ` Alexandru Stefan ISAILA
2019-07-01 14:55 ` Jan Beulich
2019-07-01 15:36 ` Alexandru Stefan ISAILA [this message]
2019-07-01 15:53 ` Jan Beulich
2019-07-02 7:58 ` Alexandru Stefan ISAILA
2019-07-02 8:01 ` Jan Beulich
2019-07-02 8:10 ` Alexandru Stefan ISAILA
2019-07-01 15:13 ` Razvan Cojocaru
2019-07-01 15:32 ` Jan Beulich
-- strict thread matches above, loose matches on Subject: below --
2019-06-04 11:49 Alexandru Stefan ISAILA
2019-06-11 12:45 ` Paul Durrant
2019-06-12 9:27 ` Alexandru Stefan ISAILA
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