[xen master] x86/cpuid: prevent decreasing of hypervisor max leaf on migration

[patchbot@xxxxxxx]

commit 6f1d6682de832d12b728f856331e700a89737a1e
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Wed Oct 27 16:00:50 2021 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Oct 29 17:42:03 2021 +0100

    x86/cpuid: prevent decreasing of hypervisor max leaf on migration
    
    In order to be compatible with previous Xen versions, and not change
    max hypervisor leaf as a result of a migration, keep the clamping of
    the maximum leaf value provided to XEN_CPUID_MAX_NUM_LEAVES, instead
    of doing it based on the domain type. Also set the default maximum
    leaf without taking the domain type into account. The maximum
    hypervisor leaf is not migrated, so we need the default to not regress
    beyond what might already be reported to a guest by existing Xen
    versions.
    
    This is a partial revert of 540d911c28 and restores the previous
    behaviour and assures that HVM guests won't see it's maximum
    hypervisor leaf reduced from 5 to 4 as a result of a migration.
    
    Fixes: 540d911c28 ('x86/CPUID: shrink max_{,sub}leaf fields according to 
actual leaf contents')
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
 xen/arch/x86/traps.c                | 6 ++----
 xen/include/public/arch-x86/cpuid.h | 6 +-----
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index a1c2adb7ad..79fd276a41 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1086,15 +1086,13 @@ void cpuid_hypervisor_leaves(const struct vcpu *v, 
uint32_t leaf,
     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;
diff --git a/xen/include/public/arch-x86/cpuid.h 
b/xen/include/public/arch-x86/cpuid.h
index 00926b1fef..ce46305bee 100644
--- 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__ */
--
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