[Xen-changelog] [xen master] tools/libxc: retry hypercall in case of EFAULT

[patchbot@xxxxxxx]

commit 988d66cb78c35c620c2a0eb01bac842e4e99bf0e
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Mon Jun 18 09:18:56 2018 +0200
Commit:     Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CommitDate: Mon Jun 18 12:31:50 2018 +0100

    tools/libxc: retry hypercall in case of EFAULT
    
    A hypercall issued via the privcmd driver can very rarely return
    -EFAULT even if the hypercall buffers are locked in memory. This
    happens for hypercall buffers in user memory when the Linux kernel
    is doing memory scans e.g. for page migration or compaction.
    
    Retry the getpageframeinfo3 hypercall up to 2 times in case
    -EFAULT is returned and the hypervisor might see invalid PTEs for
    user hypercall buffers (which should be the case only if the kernel
    doesn't offer a /dev/xen/hypercall node).
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 tools/libxc/xc_private.c |  2 +-
 tools/libxc/xc_private.h | 25 ++++++++++++++++++++++---
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c
index fcda981744..e6e3d9913c 100644
--- a/tools/libxc/xc_private.c
+++ b/tools/libxc/xc_private.c
@@ -224,7 +224,7 @@ int xc_get_pfn_type_batch(xc_interface *xch, uint32_t dom,
     domctl.domain = dom;
     domctl.u.getpageframeinfo3.num = num;
     set_xen_guest_handle(domctl.u.getpageframeinfo3.array, arr);
-    rc = do_domctl(xch, &domctl);
+    rc = do_domctl_retry_efault(xch, &domctl);
     xc_hypercall_bounce_post(xch, arr);
     return rc;
 }
diff --git a/tools/libxc/xc_private.h b/tools/libxc/xc_private.h
index 03bc9a7776..03bdfca7d4 100644
--- a/tools/libxc/xc_private.h
+++ b/tools/libxc/xc_private.h
@@ -254,9 +254,13 @@ out1:
     return ret;
 }
 
-static inline int do_domctl(xc_interface *xch, struct xen_domctl *domctl)
+static inline int do_domctl_maybe_retry_efault(xc_interface *xch,
+                                               struct xen_domctl *domctl,
+                                               unsigned int retries)
 {
     int ret = -1;
+    unsigned int retry_cnt = 0;
+
     DECLARE_HYPERCALL_BOUNCE(domctl, sizeof(*domctl), 
XC_HYPERCALL_BUFFER_BOUNCE_BOTH);
 
     domctl->interface_version = XEN_DOMCTL_INTERFACE_VERSION;
@@ -267,8 +271,11 @@ static inline int do_domctl(xc_interface *xch, struct 
xen_domctl *domctl)
         goto out1;
     }
 
-    ret = xencall1(xch->xcall, __HYPERVISOR_domctl,
-                   HYPERCALL_BUFFER_AS_ARG(domctl));
+    do {
+        ret = xencall1(xch->xcall, __HYPERVISOR_domctl,
+                       HYPERCALL_BUFFER_AS_ARG(domctl));
+    } while ( ret < 0 && errno == EFAULT && retry_cnt++ < retries );
+
     if ( ret < 0 )
     {
         if ( errno == EACCES )
@@ -281,6 +288,18 @@ static inline int do_domctl(xc_interface *xch, struct 
xen_domctl *domctl)
     return ret;
 }
 
+static inline int do_domctl(xc_interface *xch, struct xen_domctl *domctl)
+{
+    return do_domctl_maybe_retry_efault(xch, domctl, 0);
+}
+
+static inline int do_domctl_retry_efault(xc_interface *xch, struct xen_domctl 
*domctl)
+{
+    unsigned int retries = xencall_buffers_never_fault(xch->xcall) ? 0 : 2;
+
+    return do_domctl_maybe_retry_efault(xch, domctl, retries);
+}
+
 static inline int do_sysctl(xc_interface *xch, struct xen_sysctl *sysctl)
 {
     int ret = -1;
--
generated by git-patchbot for /home/xen/git/xen.git#master

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