Re: [Xen-devel] [PATCHv4 04/14] xen: remove scratch frames for ballooned pages and m2p override

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 27/01/15 10:57, Stefano Stabellini wrote:
> On Mon, 26 Jan 2015, David Vrabel wrote:
>> The scratch frame mappings for ballooned pages and the m2p override
>> are broken.  Remove them in preparation for replacing them with
>> simpler mechanisms that works.
>>
>> The scratch pages did not ensure that the page was not in use.  In
>> particular, the foreign page could still be in use by hardware.  If
>> the guest reused the frame the hardware could read or write that
>> frame.
>>
>> The m2p override did not handle the same frame being granted by two
>> different grant references.  Trying an M2P override lookup in this
>> case is impossible.
>>
>> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> [...]
> 
>>  int set_foreign_p2m_mapping(struct gnttab_map_grant_ref *map_ops,
>>                          struct gnttab_map_grant_ref *kmap_ops,
>>                          struct page **pages, unsigned int count)
>>  {
>>      int i, ret = 0;
>> -    bool lazy = false;
>>      pte_t *pte;
>>  
>>      if (xen_feature(XENFEAT_auto_translated_physmap))
>>              return 0;
>>  
>> -    if (kmap_ops &&
>> -        !in_interrupt() &&
>> -        paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
>> -            arch_enter_lazy_mmu_mode();
>> -            lazy = true;
>> +    if (kmap_ops) {
>> +            ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
>> +                                            kmap_ops, count);
>> +            if (ret)
>> +                    goto out;
>>      }
> 
> I think that you should explain why you are adding one more grant table
> mapping to a function meant to work on the p2m/m2p.  Everything else is
> clear.

I'm not.  This function has always done this.

David

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