[xen staging] tools/libxl: Work around libvirt breakage in libxl__cpuid_legacy()

[patchbot@xxxxxxx]

commit 8ef6345ef557cc2c47298217635a3088eaa59893
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Oct 2 18:23:42 2020 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Oct 2 18:57:50 2020 +0100

    tools/libxl: Work around libvirt breakage in libxl__cpuid_legacy()
    
    OSSTest reports that libvirt is reliably regressed.
    
    The only possible option is a side effect of using libxl_defbool_val(), 
which
    can only be the assert() within.  Unfortunately, libvirt actually crashes in
    __vfscanf_internal() while presumably trying to render some form of error.
    
    Open code the check without the assert() to unblock staging, while we
    investigate what is going on with libvirt.  This will want reverting at some
    point in the future.
    
    Not-really-fixes: bfcc97c08c ("tools/cpuid: Plumb nested_virt down into 
xc_cpuid_apply_policy()" reliably breaks libvirt.)
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
 tools/libs/light/libxl_cpuid.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/libs/light/libxl_cpuid.c b/tools/libs/light/libxl_cpuid.c
index 08e85dcffb..16c077cceb 100644
--- a/tools/libs/light/libxl_cpuid.c
+++ b/tools/libs/light/libxl_cpuid.c
@@ -422,7 +422,15 @@ void libxl__cpuid_legacy(libxl_ctx *ctx, uint32_t domid, 
bool restore,
 {
     bool pae = true;
     bool itsc;
-    bool nested_virt = libxl_defbool_val(info->nested_hvm);
+
+    /*
+     * Gross hack.  Using libxl_defbool_val() here causes libvirt to crash in
+     * __vfscanf_internal(), which is probably collateral damage from a side
+     * effect of the assert().
+     *
+     * Unblock things for now by opencoding without the assert.
+     */
+    bool nested_virt = info->nested_hvm.val > 0;
 
     /*
      * For PV guests, PAE is Xen-controlled (it is the 'p' that differentiates
--
generated by git-patchbot for /home/xen/git/xen.git#staging