[PATCH v1] xen/balloon: Fix mapping PG_offline pages to user space

[PATCH v1] xen/balloon: Fix mapping PG_offline pages to user space

[David Hildenbrand]

The XEN balloon driver - in contrast to other balloon drivers - allows
to map some inflated pages to user space. Such pages are allocated via
alloc_xenballooned_pages() and freed via free_xenballooned_pages().
The pfn space of these allocated pages is used to map other things
by the hypervisor using hypercalls.

Pages marked with PG_offline must never be mapped to user space (as
this page type uses the mapcount field of struct pages).

So what we can do is, clear/set PG_offline when allocating/freeing an
inflated pages. This way, most inflated pages can be excluded by
dumping tools and the "reused for other purpose" balloon pages are
correctly not marked as PG_offline.

Fixes: 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)
Reported-by: Julien Grall <julien.grall@arm.com>
Tested-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/xen/balloon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 39b229f9e256..751d32f41f26 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -604,6 +604,7 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 	while (pgno < nr_pages) {
 		page = balloon_retrieve(true);
 		if (page) {
+			__ClearPageOffline(page);
 			pages[pgno++] = page;
 #ifdef CONFIG_XEN_HAVE_PVMMU
 			/*
@@ -646,6 +647,7 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
 
 	for (i = 0; i < nr_pages; i++) {
 		if (pages[i])
+			__SetPageOffline(pages[i]);
 			balloon_append(pages[i]);
 	}
 
-- 
2.17.2

Re: [PATCH v1] xen/balloon: Fix mapping PG_offline pages to user space

[Oscar Salvador]

On Thu, Mar 14, 2019 at 04:40:25PM +0100, David Hildenbrand wrote:
> @@ -646,6 +647,7 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
>  
>  	for (i = 0; i < nr_pages; i++) {
>  		if (pages[i])
> +			__SetPageOffline(pages[i]);
>  			balloon_append(pages[i]);

didn't you forget {} there? ;-)

>  	}
>  
> -- 
> 2.17.2
> 

-- 
Oscar Salvador
SUSE L3

Re: [PATCH v1] xen/balloon: Fix mapping PG_offline pages to user space

[David Hildenbrand]

On 14.03.19 16:49, Oscar Salvador wrote:
> On Thu, Mar 14, 2019 at 04:40:25PM +0100, David Hildenbrand wrote:
>> @@ -646,6 +647,7 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
>>  
>>  	for (i = 0; i < nr_pages; i++) {
>>  		if (pages[i])
>> +			__SetPageOffline(pages[i]);
>>  			balloon_append(pages[i]);
> 
> didn't you forget {} there? ;-)
> 

That's what happens when you stashed the original patch and try to
recreate it quickly from a mail ;)

Thanks!


-- 

Thanks,

David / dhildenb

Re: [Xen-devel] [PATCH v1] xen/balloon: Fix mapping PG_offline pages to user space

[Jan Beulich]

>>> On 14.03.19 at 16:40, <david@redhat.com> wrote:
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -604,6 +604,7 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
>  	while (pgno < nr_pages) {
>  		page = balloon_retrieve(true);
>  		if (page) {
> +			__ClearPageOffline(page);
>  			pages[pgno++] = page;

While this one's fine, ...

> @@ -646,6 +647,7 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
>  
>  	for (i = 0; i < nr_pages; i++) {
>  		if (pages[i])
> +			__SetPageOffline(pages[i]);
>  			balloon_append(pages[i]);
>  	}

... I think you want to add a pair of braces here.

Jan

Re: [Xen-devel] [PATCH v1] xen/balloon: Fix mapping PG_offline pages to user space

[David Hildenbrand]

On 14.03.19 16:49, Jan Beulich wrote:
>>>> On 14.03.19 at 16:40, <david@redhat.com> wrote:
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -604,6 +604,7 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
>>  	while (pgno < nr_pages) {
>>  		page = balloon_retrieve(true);
>>  		if (page) {
>> +			__ClearPageOffline(page);
>>  			pages[pgno++] = page;
> 
> While this one's fine, ...
> 
>> @@ -646,6 +647,7 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
>>  
>>  	for (i = 0; i < nr_pages; i++) {
>>  		if (pages[i])
>> +			__SetPageOffline(pages[i]);
>>  			balloon_append(pages[i]);
>>  	}
> 
> ... I think you want to add a pair of braces here.
> 
> Jan
> 
> 

Indeed, dropped by accident. Will resend in a minute. Thanks!

-- 

Thanks,

David / dhildenb