Questions about the mapping from gpfn to mfn when live migration

Questions about the mapping from gpfn to mfn when live migration

[Kai Luo]

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Hi everyone: 
I am reading code of live migration process of hvm domain now.My question is that I can't find the transformation position that transform hvm domain‘s gpfn to mfn.That is,the method ,in file xc_linux_osdep.c, linux_privcmd_map_foreign_bulk( xc_interface *xch, xc_osdep_handle h, uint32_t dom, int prot, const xen_pfn_t *arr, int *err, unsigned int num) ,the list of xen_pfn_t contains the list of guest's mfns(gpfns in xen),for para-virtualization guests they are thransformed by the pfn_to_mfn() before assignment(in xc_domain_save())，for hvm guests however，I can not find a similar conversion process,they are directly conveyed to the dom's kernel directly without any transformation.So I continued to follow the process,finding the following key functions: 
privcmd_ioctl (struct file *file, unsigned int cmd, unsigned long data) 
->privcmd_ioctl_mmap_batch(udata, 2) 
->-> traverse_pages(mmapcmd.num, sizeof(struct privcmd_mmap_entry), &pagelist, mmap_mfn_range, &state); 
Still no clue for the thransformation process,could you give any sugguestions? 
My second question is that is it possible that I give a list of hvm's mfns(not gpfns) and then get the contents held in memory in dom0?Does xen have any function of this kind? 
Thank you all! 
Jone 

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Re: Questions about the mapping from gpfn to mfn when live migration

[Andrew Cooper]

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On 02/06/13 07:19, Kai Luo wrote:
> Hi everyone:
>     I am reading code of live migration process of hvm domain now.My
> question is that I can't find the transformation position that
> transform hvm domain‘s gpfn to mfn.That is,the method ,in file
> xc_linux_osdep.c,linux_privcmd_map_foreign_bulk(xc_interface *xch,
> xc_osdep_handle h,uint32_t dom, int prot,const xen_pfn_t *arr, int
> *err, unsigned int num),the list of xen_pfn_t contains the list of
> guest's mfns(gpfns in xen),for para-virtualization guests they are
> thransformed by the pfn_to_mfn() before assignment(in
> xc_domain_save())，for hvm guests however，I can not find a similar
> conversion process,they are directly conveyed to the dom's kernel
> directly without any transformation.So I continued to follow the
> process,finding the following key functions:
>     privcmd_ioctl(struct file *file,unsigned int cmd, unsigned long data) 
>      ->privcmd_ioctl_mmap_batch(udata, 2)
>      ->->  traverse_pages(mmapcmd.num, sizeof(struct
> privcmd_mmap_entry),&pagelist,mmap_mfn_range, &state);
>     Still no clue for the thransformation process,could you give any
> sugguestions?
>     My second question is that is it possible that I give a list of
> hvm's mfns(not gpfns) and then get the contents held in memory in
> dom0?Does xen have any function of this kind?
> Thank you all!
> Jone    

Xen does the transformation.

All mapping functions take "Guest physical addresses", i.e. the values a
guest puts in their pagetables.  For PV guests, this is MFNs but for HVM
guests, only Xen can read the EPT/NPT pagetables to transform guest
physical into host physical.

I am not aware of any supported interface which would allow dom0 to map
raw mfns, nor should there be.  What is the problem you are trying to
solve by doing this?

~Andrew

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