Re: [Xen-devel] [PATCH 2/2] Nested EPT: fixing issue of translate L2 gva to L1 gfn

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Egger, Christoph wrote on 2014-02-12:
> On 12.02.14 03:08, Yang Zhang wrote:
>> From: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>> 
>> There is no way to translate L2 gva to L1 gfn directly.
> 
> Why?

I guess you mean p2m_ga_to_gfn() is able to do it. 

> 
>> To do it, we need to get L2's gfn first. Then look up the virtual EPT
>> to get L1's gfn.
>> 
>> Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>> ---
>>  xen/arch/x86/mm/p2m.c |   25 ++++++++++++++++++++-----
>>  1 files changed, 20 insertions(+), 5 deletions(-)
>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c index
>> 8f380ed..e92cfbe 100644
>> --- a/xen/arch/x86/mm/p2m.c
>> +++ b/xen/arch/x86/mm/p2m.c
>> @@ -1605,22 +1605,37 @@ unsigned long paging_gva_to_gfn(struct vcpu
> *v,
>>          && paging_mode_hap(v->domain)
>>          && nestedhvm_is_n2(v) )
>>      {
>> -        unsigned long gfn;
>> +        unsigned long gfn, l1gfn, exit_qual;
>>          struct p2m_domain *p2m; const struct paging_mode *mode; -     
>>            uint32_t pfec_21 = *pfec; uint64_t np2m_base =
>>          nhvm_vcpu_p2m_base(v);
>> +        unsigned int page_order, exit_reason;
>> +        int rc;
>> +        uint8_t p2m_acc;
>> +        struct nestedvmx *nvmx = &vcpu_2_nvmx(v);
>> 
>>          /* translate l2 guest va into l2 guest gfn */
>>          p2m = p2m_get_nestedp2m(v, np2m_base);
>>          mode = paging_get_nestedmode(v);
>>          gfn = mode->gva_to_gfn(v, p2m, va, pfec);
>> +        if ( gfn == INVALID_GFN )
>> +            return gfn;
>> +
>>          /* translate l2 guest gfn into l1 guest gfn */
>> -        return hostmode->p2m_ga_to_gfn(v, hostp2m, np2m_base, -       
>>                                gfn << PAGE_SHIFT, &pfec_21, NULL); -   
>> }
> 
> I think in p2m-ept.c you should override that function pointer to a
> EPT specific implementation.
> 

Right. I just noticed that p2m_ga_to_gfn() is designed to do this. 

> Christoph
> 
>> +        rc = nept_translate_l2ga(v, gfn << 12 , &page_order, 4, +
>> &l1gfn, &p2m_acc, +                                &exit_qual,
>> &exit_reason); +        if ( rc == EPT_TRANSLATE_VIOLATION || rc ==
>> EPT_TRANSLATE_MISCONFIG ) +        { +            nvmx->ept.exit_reason
>> = exit_reason; +            nvmx->ept.exit_qual = exit_qual; +         
>>   vcpu_nestedhvm(current).nv_vmexit_pending = 1; +        } +        if
>> ( rc == EPT_TRANSLATE_RETRY ) +            *pfec = PFEC_page_paged;
>> 
>> +        return l1gfn;
>> +    }
>>      return hostmode->gva_to_gfn(v, hostp2m, va, pfec);  }
>>


Best regards,
Yang



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