x86/cpuid: Clobber CPUID leaves 0x800000{1d..20} in policies

c/s 1a91425 increased the AMD max leaf from 0x8000001c to 0x80000021, but
did not adjust anything in the calculate_*_policy() chain.  As a result, on
hardware supporting these leaves, we read the real hardware values into the
raw policy, then copy into host, and all the way into the PV/HVM default
policies.

All 4 of these leaves have enable bits (first two by TopoExt, next by SEV,
next by PQOS), so any software following the rules is fine and will leave them
alone.  However, leaf 0x8000001d takes a subleaf input and at least two
userspace utilities have been observed to loop indefinitely under Xen (clearly
waiting for eax to report "no more cache levels").

Such userspace is buggy, but Xen's behaviour isn't great either.

In the short term, clobber all information in these leaves.  This is a giant
bodge, but there are complexities with implementing all of these leaves
properly.

Fixes: 1a91425 ("x86/cpuid: support LFENCE always serialising CPUID bit")
Link: QubesOS/qubes-issues#7392
Reported-by: fosslinux <fosslinux@aussies.space>
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: d4012d5
master date: 2022-04-07 11:36:45 +0100

xen/arch/x86/cpuid.c

@@ -291,8 +291,15 @@ static void recalculate_misc(struct cpuid_policy *p)
 
         zero_leaves(p->extd.raw, 0xb, 0x18);
 
+        /* 0x19 - TLB details.  Pass through. */
+        /* 0x1a - Perf hints.   Pass through. */
+
         p->extd.raw[0x1b] = EMPTY_LEAF; /* IBS - not supported. */
         p->extd.raw[0x1c] = EMPTY_LEAF; /* LWP - not supported. */
+        p->extd.raw[0x1d] = EMPTY_LEAF; /* TopoExt Cache */
+        p->extd.raw[0x1e] = EMPTY_LEAF; /* TopoExt APIC ID/Core/Node */
+        p->extd.raw[0x1f] = EMPTY_LEAF; /* SEV */
+        p->extd.raw[0x20] = EMPTY_LEAF; /* Platform QoS */
         break;
     }
 }