[PATCH] x86/CPUID: don't shrink hypervisor leaves

[Jan Beulich <jbeulich@xxxxxxxx>]

This is a partial revert of 540d911c2813 ("x86/CPUID: shrink
max_{,sub}leaf fields according to actual leaf contents"). Andrew points
out that XXX.

Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Obviously the XXX wants filling in. So far I did not really understand
what bad consequences there might be, but I can agree with the undoing
of this part of the original change along the lines of why the Viridian
side adjustment was also requested to be dropped (before the patch went
in).

--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -964,15 +964,13 @@ void cpuid_hypervisor_leaves(const struc
     uint32_t base = is_viridian_domain(d) ? 0x40000100 : 0x40000000;
     uint32_t idx  = leaf - base;
     unsigned int limit = is_viridian_domain(d) ? p->hv2_limit : p->hv_limit;
-    unsigned int dflt = is_pv_domain(d) ? XEN_CPUID_MAX_PV_NUM_LEAVES
-                                        : XEN_CPUID_MAX_HVM_NUM_LEAVES;
 
     if ( limit == 0 )
         /* Default number of leaves */
-        limit = dflt;
+        limit = XEN_CPUID_MAX_NUM_LEAVES;
     else
         /* Clamp toolstack value between 2 and MAX_NUM_LEAVES. */
-        limit = min(max(limit, 2u), dflt);
+        limit = min(max(limit, 2u), XEN_CPUID_MAX_NUM_LEAVES + 0u);
 
     if ( idx > limit )
         return;
--- a/xen/include/public/arch-x86/cpuid.h
+++ b/xen/include/public/arch-x86/cpuid.h
@@ -113,10 +113,6 @@
 /* Max. address width in bits taking memory hotplug into account. */
 #define XEN_CPUID_MACHINE_ADDRESS_WIDTH_MASK (0xffu << 0)
 
-#define XEN_CPUID_MAX_PV_NUM_LEAVES 5
-#define XEN_CPUID_MAX_HVM_NUM_LEAVES 4
-#define XEN_CPUID_MAX_NUM_LEAVES \
-    (XEN_CPUID_MAX_PV_NUM_LEAVES > XEN_CPUID_MAX_HVM_NUM_LEAVES ? \
-     XEN_CPUID_MAX_PV_NUM_LEAVES : XEN_CPUID_MAX_HVM_NUM_LEAVES)
+#define XEN_CPUID_MAX_NUM_LEAVES 5
 
 #endif /* __XEN_PUBLIC_ARCH_X86_CPUID_H__ */