Xen project Mailing List

On Wed, Apr 27, 2016 at 9:31 AM, George Dunlap <george.dunlap@xxxxxxxxxx> wrote:

On 27/04/16 16:18, Tamas K Lengyel wrote:
> On Wed, Apr 27, 2016 at 9:01 AM, George Dunlap <george.dunlap@xxxxxxxxxx>
> wrote:
>
>> On 21/04/16 18:10, Tamas K Lengyel wrote:
>>> Don't propagate altp2m changes from ept_set_entry for memshare as
>> memshare
>>> already has the lock. We call altp2m propagate changes once memshare
>>> successfully finishes. Also, allow the hostp2m entries to be of type
>>> p2m_ram_shared.
>>>
>>> Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
>>
>> Sorry for the delay in reviewing -- trying to get my head back around
>> the altp2m code. On the whole looks reasonable, but one question...
>>
>>> ---
>>> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>>> Cc: Keir Fraser <keir@xxxxxxx>
>>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
>>> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
>>> ---
>>> xen/arch/x86/mm/mem_sharing.c | 11 +++++++++++
>>> xen/arch/x86/mm/p2m-ept.c | 2 +-
>>> xen/arch/x86/mm/p2m.c | 7 +++----
>>> 3 files changed, 15 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/xen/arch/x86/mm/mem_sharing.c
>> b/xen/arch/x86/mm/mem_sharing.c
>>> index a522423..d5b4b2d 100644
>>> --- a/xen/arch/x86/mm/mem_sharing.c
>>> +++ b/xen/arch/x86/mm/mem_sharing.c
>>> @@ -35,6 +35,7 @@
>>> #include <asm/p2m.h>
>>> #include <asm/atomic.h>
>>> #include <asm/event.h>
>>> +#include <asm/altp2m.h>
>>> #include <xsm/xsm.h>
>>>
>>> #include "mm-locks.h"
>>> @@ -1026,6 +1027,16 @@ int mem_sharing_share_pages(struct domain *sd,
>> unsigned long sgfn, shr_handle_t
>>> /* We managed to free a domain page. */
>>> atomic_dec(&nr_shared_mfns);
>>> atomic_inc(&nr_saved_mfns);
>>> +
>>> + if( altp2m_active(cd) )
>>> + {
>>> + p2m_access_t a;
>>> + struct p2m_domain *p2m = p2m_get_hostp2m(cd);
>>> + p2m->get_entry(p2m, cgfn, NULL, &a, 0, NULL, NULL);
>>> + p2m_altp2m_propagate_change(cd, _gfn(cgfn), smfn, PAGE_ORDER_4K,
>>> + p2m_ram_shared, a);
>>> + }
>>> +
>>> ret = 0;
>>>
>>> err_out:
>>> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
>>> index 3cb6868..1ac3018 100644
>>> --- a/xen/arch/x86/mm/p2m-ept.c
>>> +++ b/xen/arch/x86/mm/p2m-ept.c
>>> @@ -846,7 +846,7 @@ out:
>>> if ( is_epte_present(&old_entry) )
>>> ept_free_entry(p2m, &old_entry, target);
>>>
>>> - if ( rc == 0 && p2m_is_hostp2m(p2m) )
>>> + if ( rc == 0 && p2m_is_hostp2m(p2m) && p2mt != p2m_ram_shared )
>>> p2m_altp2m_propagate_change(d, _gfn(gfn), mfn, order, p2mt,
>> p2ma);
>>>
>>> return rc;
>>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
>>> index b3fce1b..d2aebf7 100644
>>> --- a/xen/arch/x86/mm/p2m.c
>>> +++ b/xen/arch/x86/mm/p2m.c
>>> @@ -1739,11 +1739,10 @@ int p2m_set_altp2m_mem_access(struct domain *d,
>> struct p2m_domain *hp2m,
>>> /* Check host p2m if no valid entry in alternate */
>>> if ( !mfn_valid(mfn) )
>>> {
>>> - mfn = hp2m->get_entry(hp2m, gfn_l, &t, &old_a,
>>> - P2M_ALLOC | P2M_UNSHARE, &page_order,
>> NULL);
>>> + mfn = hp2m->get_entry(hp2m, gfn_l, &t, &old_a, 0, &page_order,
>> NULL);
>>
>> Why are you getting rid of P2M_ALLOC here? What happens if the hp2m
>> entry is populate-on-demand?
>>
>
> There is a check further down here that only allows p2m_ram_rw and
> p2m_ram_shared.

So what P2M_ALLOC means is, "If this is entry is PoD, then please
populate it so I get a ram page." So the only way you can get a
p2m_populate_on_demand type returned is if you remove this flag. Leave
it and (assuming there's enough ram to go around), you'll always get
p2m_ram_rw. :-)

> On the non-altp2m path mem_access doesn't request P2M_ALLOC
> either (but doesn't check the type), so I would say mem_access is not
> compatible with PoD.

Off the top of my head I can't see a reason why they couldn't co-exist
in principle, if you added P2M_ALLOC in a few key places.

Sure, I just rather do that in a separate patch and for now have the mem_access paths behaving the same way before doing that adjustment.

Tamas

Re: [Xen-devel] [PATCH] altp2m: Allow the hostp2m to be shared