From: "Egger, Christoph" <chegger@amazon.de>
To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: hap_invlpg() vs INVLPGA
Date: Fri, 29 Jan 2016 18:09:45 +0100 [thread overview]
Message-ID: <56AB9CD9.8070103@amazon.de> (raw)
In-Reply-To: <56AB992202000078000CC72C@prv-mh.provo.novell.com>
On 29/01/16 16:53, Jan Beulich wrote:
>>>> On 29.01.16 at 15:02, <chegger@amazon.de> wrote:
>> On 29/01/16 14:57, Egger, Christoph wrote:
>>> On 29/01/16 14:24, Jan Beulich wrote:
>>>> Christoph,
>>>>
>>>> in commit dd6de3ab99 ("Implement Nested-on-Nested") you added
>>>> code to hap_invlpg() supposedly emulating INVLPGA. I've been
>>>> stumbling across this a number of times in the past, not being able
>>>> to make the connection between (a) VMX/EPT and INVLPGA and
>>>> (b) SVM's INVLPGA intercept and this function.
>>>
>>> When you boot Windows 7 as L1 guest and XP-Mode as L2 guest then
>>> L2 guest uses INVLPG instruction to invalidate a page and L1 guest
>>> handles this via using INVLPGA instruction.
>>>
>>> The INVLPG intercept flushes the nested hap p2m which is effectively
>>> a TLB flush to the L1 guest.
>>
>> ... actually to the L2 guest. Sorry for the typo.
>
> So if the L1 guest does an INVLPGA, we should see an INVLPGA
> intercept, not an INVLPG one.
INVLPG intercept comes first from L2 then INVLPGA from L1.
>>> Then this intercept is injected into L1 guest.
>
> This, otoh, reads as if you imply we intercept the L2's INVLPG.
> Yet the INVLPG intercept gets cleared when the domain uses
> NPT (and your original change also didn't alter any intercept
> settings). Hence I'm still lost how hap_invlpg() can be reached
> in that case other than via emulating INVLPG in the instruction
> emulator.
svm_invlpg_intercept() and vmx_invlpg_intercept() call
paging_invlpg(). paging_invlpg() calls hap_invlpg()
as initialized in xen/arch/x86/mm/hap/hap.c
>>> The INVLPGA instruction enforces a new ASID.
>>>
>>> If the nested hap p2m is NULL then p2m_flush() should effectively
>>> be a noop but it may not crash the guest.
>
> s/may not/should not/ ?
Yes.
Christoph
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B
next prev parent reply other threads:[~2016-01-29 17:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-29 13:24 hap_invlpg() vs INVLPGA Jan Beulich
2016-01-29 13:57 ` Egger, Christoph
2016-01-29 14:02 ` Egger, Christoph
2016-01-29 15:53 ` Jan Beulich
2016-01-29 17:09 ` Egger, Christoph [this message]
2016-02-01 8:04 ` Jan Beulich
2016-02-01 8:14 ` Egger, Christoph
2016-02-01 9:00 ` Jan Beulich
2016-02-01 9:41 ` Egger, Christoph
2016-02-01 9:58 ` Jan Beulich
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