[Xen-changelog] [xen master] x86/domctl: generalize the restore of vMCE parameters

[patchbot@xxxxxxx]

commit 862c83e90e80c1da126990a9e749338f1ee56bca
Author:     Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
AuthorDate: Fri Jul 14 12:42:35 2017 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Jul 14 12:42:35 2017 +0200

    x86/domctl: generalize the restore of vMCE parameters
    
    vMCE parameters in struct xen_domctl_ext_vcpucontext were extended in
    the past, and is likely to be extended in the future. When migrating a
    PV domain from old Xen, XEN_DOMCTL_set_ext_vcpucontext should handle
    the differences.
    
    Instead of adding ad-hoc handling code at each extension, we introduce
    an array to record sizes of the current and all past versions of vMCE
    parameters, and search for the largest one that does not expire the
    size of passed-in parameters to determine vMCE parameters that will be
    restored. If vMCE parameters are extended in the future, we only need
    to adapt the array to reflect the extension.
    
    Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/domctl.c | 55 +++++++++++++++++++++++++++++++++++----------------
 1 file changed, 38 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 7fa58b4..60d95fe 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -302,6 +302,43 @@ static int update_domain_cpuid_info(struct domain *d,
     return 0;
 }
 
+static int vcpu_set_vmce(struct vcpu *v,
+                         const struct xen_domctl_ext_vcpucontext *evc)
+{
+    /*
+     * Sizes of vMCE parameters used by the current and past versions
+     * of Xen in descending order. If vMCE parameters are extended,
+     * remember to add the old size to this array by VMCE_SIZE().
+     */
+#define VMCE_SIZE(field) \
+    (offsetof(typeof(evc->vmce), field) + sizeof(evc->vmce.field))
+
+    static const unsigned int valid_sizes[] = {
+        sizeof(evc->vmce),
+        VMCE_SIZE(caps),
+    };
+#undef VMCE_SIZE
+
+    struct hvm_vmce_vcpu vmce = { };
+    unsigned int evc_vmce_size =
+        min(evc->size - offsetof(typeof(*evc), vmce), sizeof(evc->vmce));
+    unsigned int i = 0;
+
+    BUILD_BUG_ON(offsetof(typeof(*evc), mcg_cap) !=
+                 offsetof(typeof(*evc), vmce.caps));
+    BUILD_BUG_ON(sizeof(evc->mcg_cap) != sizeof(evc->vmce.caps));
+
+    while ( i < ARRAY_SIZE(valid_sizes) && evc_vmce_size < valid_sizes[i] )
+        ++i;
+
+    if ( i == ARRAY_SIZE(valid_sizes) )
+        return 0;
+
+    memcpy(&vmce, &evc->vmce, valid_sizes[i]);
+
+    return vmce_restore_vcpu(v, &vmce);
+}
+
 void arch_get_domain_info(const struct domain *d,
                           struct xen_domctl_getdomaininfo *info)
 {
@@ -912,23 +949,7 @@ long arch_do_domctl(
             else
                 domain_pause(d);
 
-            BUILD_BUG_ON(offsetof(struct xen_domctl_ext_vcpucontext,
-                                  mcg_cap) !=
-                         offsetof(struct xen_domctl_ext_vcpucontext,
-                                  vmce.caps));
-            BUILD_BUG_ON(sizeof(evc->mcg_cap) != sizeof(evc->vmce.caps));
-            if ( evc->size >= offsetof(typeof(*evc), vmce) +
-                              sizeof(evc->vmce) )
-                ret = vmce_restore_vcpu(v, &evc->vmce);
-            else if ( evc->size >= offsetof(typeof(*evc), mcg_cap) +
-                                   sizeof(evc->mcg_cap) )
-            {
-                struct hvm_vmce_vcpu vmce = { .caps = evc->mcg_cap };
-
-                ret = vmce_restore_vcpu(v, &vmce);
-            }
-            else
-                ret = 0;
+            ret = vcpu_set_vmce(v, evc);
 
             domain_unpause(d);
         }
--
generated by git-patchbot for /home/xen/git/xen.git#master

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