[xen staging] x86/mem-paging: further adjustments to p2m_mem_paging_prep()'s error handling

[patchbot@xxxxxxx]

commit cdea123f1976549ecc72644588cc5ce1491606c4
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed May 20 12:49:28 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed May 20 12:49:28 2020 +0200

    x86/mem-paging: further adjustments to p2m_mem_paging_prep()'s error 
handling
    
    Address late comments on ecb913be4aaa ("x86/mem-paging: correct
    p2m_mem_paging_prep()'s error handling"):
    - insert a gprintk() ahead of domain_crash(),
    - add a comment.
    
    Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm/mem_paging.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/arch/x86/mm/mem_paging.c b/xen/arch/x86/mm/mem_paging.c
index 6aa1bffa65..01281f786e 100644
--- a/xen/arch/x86/mm/mem_paging.c
+++ b/xen/arch/x86/mm/mem_paging.c
@@ -385,6 +385,9 @@ static int prepare(struct domain *d, gfn_t gfn,
              * The domain can't possibly know about this page yet, so failure
              * here is a clear indication of something fishy going on.
              */
+            gprintk(XENLOG_ERR,
+                    "%pd: fresh page for GFN %"PRI_gfn" in unexpected state\n",
+                    d, gfn_x(gfn));
             domain_crash(d);
             page = NULL;
             goto out;
@@ -423,6 +426,10 @@ static int prepare(struct domain *d, gfn_t gfn,
 
     if ( page )
     {
+        /*
+         * Free the page on error.  Drop our temporary reference in all
+         * cases.
+         */
         if ( ret )
             put_page_alloc_ref(page);
         put_page(page);
--
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