Re: [PATCH v1] x86/hvm: Generic instruction re-execution mechanism for execute faults

From: Razvan Cojocaru <rcojocaru@bitdefender.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Andrei LUTAS <vlutas@bitdefender.com>,
	Tamas K Lengyel <tamas@tklengyel.com>,
	Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Mihai Dontu <mdontu@bitdefender.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	aisaila@bitdefender.com,
	xen-devel <xen-devel@lists.xenproject.org>,
	Anshul Makkar <anshul.makkar@citrix.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH v1] x86/hvm: Generic instruction re-execution mechanism for execute faults
Date: Tue, 27 Nov 2018 13:44:09 +0200	[thread overview]
Message-ID: <04bd4ccd-c6d5-4891-7b20-0cc185c8f34c@bitdefender.com> (raw)
In-Reply-To: <5BFD2A520200007800200528@prv1-mh.provo.novell.com>

>> About the emulator and events: if we could have a toggle for the
>> emulator to tell it "emulate the current instruction and send out a
>> vm_event only if it touches a protected page that's NOT part of the page
>> walk", that would also work - though I can't at this point tell how
>> feasible those modifications are.
> 
> For the emulation paths it is certainly possible to have controls for
> (almost) everything, if needed. So going that route continues to
> look more desirable to me than going the route you've chosen.

It does sound very reasonable, we'll look into that.

>> The bigger practical problem is having something that works with older
>> Xen versions - for example current XenServer releases are still on Xen
>> 4.7, and backporting the whole emulator machinery there is not
>> reasonable, with the large number of changes that have occured in the
>> meantime.
>
> Well - wouldn't this apply to extensive altp2m changes as well?

It does, however for one, for some reason the altp2m patches have so far
proven (for us at least) much easier to backport (and there's less of them).

However, you do make a good point, and assuming this works emulator
changes do seem to potentially solve the problem we're having in a way
that's acceptable to everyone and is architecturally correct.

Thanks,
Razvan

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