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

From: "Jan Beulich" <JBeulich@suse.com>
To: aisaila@bitdefender.com
Cc: Andrei LUTAS <vlutas@bitdefender.com>,
	Tamas K Lengyel <tamas@tklengyel.com>,
	Wei Liu <wei.liu2@citrix.com>,
	Razvan Cojocaru <rcojocaru@bitdefender.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>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH v1] x86/hvm: Generic instruction re-execution mechanism for execute faults
Date: Thu, 20 Dec 2018 02:07:46 -0700	[thread overview]
Message-ID: <5C1B5BE20200007800207EF5@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <0D3C56BA0200004834861ACF@prv1-mh.provo.novell.com>

>>> On 19.12.18 at 17:49, <aisaila@bitdefender.com> wrote:
> On 27.11.2018 13:32, Roger Pau Monné wrote:
>> Would it be possible to add some kind of flag to the emulator to
>> signal whether p2m restrictions should be enforced/ignored?
>> hvmemul_acquire_page seems like a suitable place, but I'm not that
>> familiar with the emulator.
>> 
>> Then you could generate vm events from the emulator itself, which
>> AFAICT is the only way to handle this instruction execution issue.
> 
> I've been testing what place would be the best to have the emulator send 
> a event and it turns out the hvmemul_acquire_page is not ok. What worked 
> form me was having the emulator send write access violations from 
> hvmemul_map_linear_addr(). Here I can get the gfn, gla and offset for 
> the event.
> 
> For the exec access violation I've tried to send events from 
> hvmemul_insn_fetch() but there is a problem to get the same variables 
> for the event. Is there a way to go around and get those params for the 
> event? Any thoughts are appreciated.

One question is whether __hvmemul_read() couldn't / shouldn't
also be switched to use hvmemul_map_linear_addr(), which would
allow your insertion to live in one central place.

Jan

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