Re: [PATCH 1/4] expand x86 arch_shared_info to support linear p2m list

[Juergen Gross <jgross@suse.com>]

On 11/21/2014 01:23 PM, Jan Beulich wrote:
>>>> On 14.11.14 at 10:37, <"jgross@suse.com".non-mime.internet> wrote:
>> --- a/xen/include/public/arch-x86/xen.h
>> +++ b/xen/include/public/arch-x86/xen.h
>> @@ -224,7 +224,12 @@ struct arch_shared_info {
>>       /* Frame containing list of mfns containing list of mfns containing p2m. */
>>       xen_pfn_t     pfn_to_mfn_frame_list_list;
>>       unsigned long nmi_reason;
>> -    uint64_t pad[32];
>> +    /*
>> +     * Following two fields are valid if pfn_to_mfn_frame_list_list contains
>> +     * ~0UL.
>> +     */
>> +    unsigned long p2m_vaddr;    /* virtual address of the p2m list */
>> +    unsigned long p2m_as_root;  /* mfn of the top level page table */
>
> xen_pfn_t please. And what does the "as" in the name stand for?

"as" is address space. I can rename it to e.g. "p2m_pgd_mfn".

> It's also kind of unclear in the description what "the page table root"
> is, as I don't think there are many OSes which use just a single set
> of page tables (i.e. just a single address space). Not having followed
> the discussion closely - what is this needed for anyway?

It's a replacement of the pfn_to_mfn_frame_list_list using the same
page table as the kernel for accessing the p2m list. We need the root
of the page table and the virtual address of the p2m list.

>
>> --- a/xen/include/public/features.h
>> +++ b/xen/include/public/features.h
>> @@ -99,6 +99,9 @@
>>   #define XENFEAT_grant_map_identity        12
>>    */
>>
>> +/* x86: guest may specify virtual address of p2m list */
>> +#define XENFEAT_virtual_p2m               13
>
> The name to me suggests something that's not real. Perhaps better
> XENFEAT_virtually_mapped_p2m or XENFEAT_p2m_va{,ddr}?

Yeah, that's better. I'll use XENFEAT_p2m_vaddr.


Juergen