[PATCH] xen/tmem: Don't use map_domain_page for long-life-time pages.

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

When using tmem with Xen 4.3 (and debug build) we end up with:

(XEN) Xen BUG at domain_page.c:143
(XEN) ----[ Xen-4.3-unstable  x86_64  debug=y  Not tainted ]----
(XEN) CPU:    3
(XEN) RIP:    e008:[<ffff82c4c01606a7>] map_domain_page+0x61d/0x6e1
.. 
(XEN) Xen call trace:
(XEN)    [<ffff82c4c01606a7>] map_domain_page+0x61d/0x6e1
(XEN)    [<ffff82c4c01373de>] cli_get_page+0x15e/0x17b
(XEN)    [<ffff82c4c01377c4>] tmh_copy_from_client+0x150/0x284
(XEN)    [<ffff82c4c0135929>] do_tmem_put+0x323/0x5c4
(XEN)    [<ffff82c4c0136510>] do_tmem_op+0x5a0/0xbd0
(XEN)    [<ffff82c4c022391b>] syscall_enter+0xeb/0x145
(XEN)

A bit of debugging revealed that the map_domain_page and unmap_domain_page
are meant for short life-time mappings. And that those mappings are finite.
In the 2 VCPU guest we only have 32 entries and once we have exhausted those
we trigger the BUG_ON condition.

The two functions - tmh_persistent_pool_page_[get,put] are used by the xmem_pool
when xmem_pool_[alloc,free] are called. These xmem_pool_* function are wrapped
in macro and functions - the entry points are via: tmem_malloc
and tmem_page_alloc. In both cases the users are in the hypervisor and they
do not seem to suffer from using the hypervisor virtual addresses.

CC: Bob Liu <bob.liu@oracle.com>
CC: Dan Magenheimer <dan.magenheimer@oracle.com>
Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 xen/common/tmem_xen.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/xen/common/tmem_xen.c b/xen/common/tmem_xen.c
index 3a1f3c9..736a8c3 100644
--- a/xen/common/tmem_xen.c
+++ b/xen/common/tmem_xen.c
@@ -385,7 +385,7 @@ static void *tmh_persistent_pool_page_get(unsigned long size)
     if ( (pi = _tmh_alloc_page_thispool(d)) == NULL )
         return NULL;
     ASSERT(IS_VALID_PAGE(pi));
-    return __map_domain_page(pi);
+    return page_to_virt(pi);
 }
 
 static void tmh_persistent_pool_page_put(void *page_va)
@@ -393,8 +393,7 @@ static void tmh_persistent_pool_page_put(void *page_va)
     struct page_info *pi;
 
     ASSERT(IS_PAGE_ALIGNED(page_va));
-    pi = mfn_to_page(domain_page_map_to_mfn(page_va));
-    unmap_domain_page(page_va);
+    pi = mfn_to_page(virt_to_mfn(page_va));
     ASSERT(IS_VALID_PAGE(pi));
     _tmh_free_page_thispool(pi);
 }
-- 
1.7.7.6