Re: [Xen-devel] [PATCH v4 13/18] x86/mem_sharing: Skip xen heap pages in memshr nominate
On Mon, Jan 20, 2020 at 9:23 AM Jan Beulich wrote:
>
> On 08.01.2020 18:14, Tamas K Lengyel wrote:
> > Trying to share these would fail anyway, better to skip them early.
> >
> > Signed-off-by: Tamas K Lengyel
>
> Reviewed-by: Jan Beulich
> albeit I wonder if this couldn't be further generalized by ...
>
> > --- a/xen/arch/x86/mm/mem_sharing.c
> > +++ b/xen/arch/x86/mm/mem_sharing.c
> > @@ -852,6 +852,11 @@ static int nominate_page(struct domain *d, gfn_t gfn,
> > if ( !p2m_is_sharable(p2mt) )
> > goto out;
> >
> > +/* Skip xen heap pages */
> > +page = mfn_to_page(mfn);
> > +if ( !page || is_xen_heap_page(page) )
> > +goto out;
>
> ... checking for a zero type ref count (the only means to permit
> a type change) here, and maybe also ->count_info to fit what
> page_make_sharable() expects.
Not sure I follow you, type count is checked by page_make_sharable but
it has to be exactly 1:
/* Check if page is already typed and bail early if it is */
if ( (page->u.inuse.type_info & PGT_count_mask) != 1 )
{
spin_unlock(>page_alloc_lock);
return -EEXIST;
}
I specifically want to avoid calling page_make_sharable on xen heap
pages because they end up printing an error to the console which is
very annoying.
Tamas
___
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
Re: [Xen-devel] [PATCH v4 13/18] x86/mem_sharing: Skip xen heap pages in memshr nominate
On 20.01.2020 17:32, Tamas K Lengyel wrote:
> On Mon, Jan 20, 2020 at 9:23 AM Jan Beulich wrote:
>>
>> On 08.01.2020 18:14, Tamas K Lengyel wrote:
>>> Trying to share these would fail anyway, better to skip them early.
>>>
>>> Signed-off-by: Tamas K Lengyel
>>
>> Reviewed-by: Jan Beulich
>> albeit I wonder if this couldn't be further generalized by ...
>>
>>> --- a/xen/arch/x86/mm/mem_sharing.c
>>> +++ b/xen/arch/x86/mm/mem_sharing.c
>>> @@ -852,6 +852,11 @@ static int nominate_page(struct domain *d, gfn_t gfn,
>>> if ( !p2m_is_sharable(p2mt) )
>>> goto out;
>>>
>>> +/* Skip xen heap pages */
>>> +page = mfn_to_page(mfn);
>>> +if ( !page || is_xen_heap_page(page) )
>>> +goto out;
>>
>> ... checking for a zero type ref count (the only means to permit
>> a type change) here, and maybe also ->count_info to fit what
>> page_make_sharable() expects.
>
> Not sure I follow you, type count is checked by page_make_sharable but
> it has to be exactly 1:
>
> /* Check if page is already typed and bail early if it is */
> if ( (page->u.inuse.type_info & PGT_count_mask) != 1 )
> {
> spin_unlock(>page_alloc_lock);
> return -EEXIST;
> }
Which is after a successful get_page_and_type(). Prior to that,
therefore, the count ought to be zero. But maybe I'm very confused
- see also my comments on patch 14, where I spotted this very same
anomaly.
> I specifically want to avoid calling page_make_sharable on xen heap
> pages because they end up printing an error to the console which is
> very annoying.
That's fine. I'm not asking to drop what you're doing. Instead I'm
asking whether you couldn't bail early in even more cases.
Jan
___
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
Re: [Xen-devel] [PATCH v4 13/18] x86/mem_sharing: Skip xen heap pages in memshr nominate
On 08.01.2020 18:14, Tamas K Lengyel wrote: > Trying to share these would fail anyway, better to skip them early. > > Signed-off-by: Tamas K Lengyel Reviewed-by: Jan Beulich albeit I wonder if this couldn't be further generalized by ... > --- a/xen/arch/x86/mm/mem_sharing.c > +++ b/xen/arch/x86/mm/mem_sharing.c > @@ -852,6 +852,11 @@ static int nominate_page(struct domain *d, gfn_t gfn, > if ( !p2m_is_sharable(p2mt) ) > goto out; > > +/* Skip xen heap pages */ > +page = mfn_to_page(mfn); > +if ( !page || is_xen_heap_page(page) ) > +goto out; ... checking for a zero type ref count (the only means to permit a type change) here, and maybe also ->count_info to fit what page_make_sharable() expects. Jan ___ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
[Xen-devel] [PATCH v4 13/18] x86/mem_sharing: Skip xen heap pages in memshr nominate
Trying to share these would fail anyway, better to skip them early.
Signed-off-by: Tamas K Lengyel
---
xen/arch/x86/mm/mem_sharing.c | 6 +-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index b8a9228ecf..baa3e35ded 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -852,6 +852,11 @@ static int nominate_page(struct domain *d, gfn_t gfn,
if ( !p2m_is_sharable(p2mt) )
goto out;
+/* Skip xen heap pages */
+page = mfn_to_page(mfn);
+if ( !page || is_xen_heap_page(page) )
+goto out;
+
/* Check if there are mem_access/remapped altp2m entries for this page */
if ( altp2m_active(d) )
{
@@ -882,7 +887,6 @@ static int nominate_page(struct domain *d, gfn_t gfn,
}
/* Try to convert the mfn to the sharable type */
-page = mfn_to_page(mfn);
ret = page_make_sharable(d, page, expected_refcnt);
if ( ret )
goto out;
--
2.20.1
___
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
