Re: [Xen-devel] [PATCH 09/22] vixen: modify the e820 table to advertise HVM special pages as RAM

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/01/2018 09:51, Roger Pau Monné wrote:
> On Sun, Jan 07, 2018 at 07:27:48AM -0800, Anthony Liguori wrote:
>> On Sun, Jan 7, 2018 at 12:16 AM, Roger Pau Monné <roger.pau@xxxxxxxxxx> 
>> wrote:
>>> On Sat, Jan 06, 2018 at 02:54:24PM -0800, Anthony Liguori wrote:
>>>> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
>>>> index a56f875..935901b 100644
>>>> --- a/xen/arch/x86/mm.c
>>>> +++ b/xen/arch/x86/mm.c
>>>> @@ -122,6 +122,7 @@
>>>>  #include <asm/fixmap.h>
>>>>  #include <asm/io_apic.h>
>>>>  #include <asm/pci.h>
>>>> +#include <asm/guest.h>
>>>>
>>>>  #include <asm/hvm/grant_table.h>
>>>>  #include <asm/pv/grant_table.h>
>>>> @@ -945,7 +946,7 @@ get_page_from_l1e(
>>>>              case 0:
>>>>                  break;
>>>>              case 1:
>>>> -                if ( !is_hardware_domain(l1e_owner) )
>>>> +                if ( !is_vixen() && !is_hardware_domain(l1e_owner) )
>>>>                      break;
>>>>                  /* fallthrough */
>>>>              case -1:
>>>> @@ -5536,6 +5537,21 @@ void arch_dump_shared_mem_info(void)
>>>>              mem_sharing_get_nr_saved_mfns());
>>>>  }
>>>>
>>>> +const unsigned long *__init
>>>> +vixen_get_platform_badpages(unsigned int *array_size)
>>>> +{
>>>> +    static unsigned long __initdata bad_pages[] = {
>>>> +        0xfeffc000,
>>>> +        0xfeffd000,
>>>> +        0xfeffe000,
>>>> +        0xfefff000,
>>> This values shouldn't be hardcoded. IMHO it would also be good to
>>> place all the vixen_ helpers in a single file.
>> Ack on moving to a helper.
>>
>> I don't know of a way to call the hypervisor to ask "what's the
>> special page range?".  I can find special pages via the hvm get
>> parameters calls but there's no guarantee they are contiguous so the
>> resulting code to punch holes in the e820 because fairly complex.  Any
>> ideas how to do this nicely?
> I've done something similar for the shim, but the values in the
> bag_pages array are dynamic:
>
> http://xenbits.xen.org/gitweb/?p=people/liuw/xen.git;a=commit;h=d5a72acaa2ced1bd66a1ef1ef7a4a1bda43a9df3
>
> Also, why do you need to add 4 GFNs to the list of bad pages? Just
> adding the console/xenstore pages to the e820 and to the list of bad
> pages should be enough.

You've got to be careful not to have the bootscrub zero the IDENT_PT. 
For safety, I put all of the special pages through this E820/bad cycle.

~Andrew

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