Re: [Xen-devel] hap_invlpg() vs INVLPGA

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.01.16 at 15:02, <chegger@xxxxxxxxx> 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.

>> 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.

>> 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/ ?

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel