[Xen-devel] [PATCH] xen/p2m: Don't call get_balloon_scratch_page() twice, keep interrupts disabled for multicalls

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

m2p_remove_override() calls get_balloon_scratch_page() in
MULTI_update_va_mapping() even though it already has pointer to this page from
the earlier call (in scratch_page). This second call doesn't have a matching
put_balloon_scratch_page() thus not restoring preempt count back. (Also, there
is no put_balloon_scratch_page() in the error path.)

In addition, the second multicall uses __xen_mc_entry() which does not disable
interrupts. Rearrange xen_mc_* calls to keep interrupts off while performing
multicalls.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 arch/x86/xen/p2m.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 0d4ec35..8b901e8 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -990,10 +990,13 @@ int m2p_remove_override(struct page *page,
                                printk(KERN_WARNING "m2p_remove_override: "
                                                "pfn %lx mfn %lx, failed to 
modify kernel mappings",
                                                pfn, mfn);
+                               put_balloon_scratch_page();
                                return -1;
                        }
 
-                       mcs = xen_mc_entry(
+                       xen_mc_batch();
+
+                       mcs = __xen_mc_entry(
                                        sizeof(struct 
gnttab_unmap_and_replace));
                        unmap_op = mcs.args;
                        unmap_op->host_addr = kmap_op->host_addr;
@@ -1003,12 +1006,11 @@ int m2p_remove_override(struct page *page,
                        MULTI_grant_table_op(mcs.mc,
                                        GNTTABOP_unmap_and_replace, unmap_op, 
1);
 
-                       xen_mc_issue(PARAVIRT_LAZY_MMU);
-
                        mcs = __xen_mc_entry(0);
                        MULTI_update_va_mapping(mcs.mc, scratch_page_address,
-                                       
pfn_pte(page_to_pfn(get_balloon_scratch_page()),
+                                       pfn_pte(page_to_pfn(scratch_page),
                                        PAGE_KERNEL_RO), 0);
+
                        xen_mc_issue(PARAVIRT_LAZY_MMU);
 
                        kmap_op->host_addr = 0;
-- 
1.8.3.1


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