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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.01.16 at 18:09, <chegger@xxxxxxxxx> wrote:
> On 29/01/16 16:53, Jan Beulich wrote:
>>>>> 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.
> 
> INVLPG intercept comes first from L2 then INVLPGA from L1.

I.e. Xen's action should be in response to the intercepted INVLPGA,
which afaict wouldn't lead to hap_invlpg().

>>>> 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

That's all fine, but according to my previous reply: How does
execution reach svm_invlpg_intercept() when the INVLPG
intercept gets disabled for domains using HAP (NPT)?

Jan


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