RE: [Xen-devel] [PATCH][VT] Patch to allow VMX domainsto be destroyedor shut down cleanly

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Hi, Keir
        Do you mean a patch like this?

Thanks
Yunhong Jiang

--- a/xen/arch/x86/vmx.c        Mon Sep 19 13:24:31 2005
+++ b/xen/arch/x86/vmx.c        Tue Sep 20 16:47:34 2005
@@ -1100,6 +1100,10 @@
                     d->arch.arch_vmx.cpu_cr3, mfn);
     }

+    if(!((value & X86_CR0_PE) && (value & X86_CR0_PG)) && paging_enabled)
+        if(d->arch.arch_vmx.cpu_cr3)
+            put_page(pfn_to_page(get_mfn_from_pfn(
+                  d->arch.arch_vmx.cpu_cr3 >> PAGE_SHIFT)));
     /*
      * VMX does not implement real-mode virtualization. We emulate
      * real-mode by performing a world switch to VMXAssist whenever


Keir Fraser wrote:
> On 19 Sep 2005, at 11:52, Jiang, Yunhong wrote:
> 
>>> I think it's more correct to do get/put in vmx_set_cr0 (at that
>>> point we can know what format the pagetables should be, for example
>>> (32/32p/64). But I think it's a bigger cleanup patch.
>> 
>> Do you mean put all get/put on vmx_set_cr0 ? even for paging enabled
>> case?
> 
> No, I mean that get/put on cr3 change (or guest destruction) should be
> gated on CR0_PG. Then, additionally, get or put is required when
> CR0_PG is toggled.
> 
>> And there is one more issue .If the guest is destroyed before the
>> kernel enabling paging, how about the page pointed by cr3? It may
>> cause one referece count left. The reason is, currently when destroy
>> domain, only domain->guest_table is released. However, if the paging
>> is not enabled, then the get_page on vmx_set_cr0 has no corresponding
>> put_page, which may cause problem. Hope comments on this point.
> 
> Doing what I describe above would fix this: CR0_PG would be clear, so
> put_page() would not happen.
> 
>>> 
>>> Whatever you go for: please send a complete tested patch. :-)
>> 
>> Sure！
> 
> Thanks!
> 
>   -- Keir


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