x86/PVH: expose OEMx ACPI tables to Dom0

What they contain we don't know, but we can't sensibly hide them. On my
Skylake system OEM1 (with a description of "INTEL  CPU EIST") is what
contains all the _PCT, _PPC, and _PSS methods, i.e. about everything
needed for cpufreq. (_PSD interestingly are in an SSDT there.)

Further OEM2 there has a description of "INTEL  CPU  HWP", while OEM4
has "INTEL  CPU  CST". Pretty clearly all three need exposing for
cpufreq and cpuidle to work.

Fixes: 8b1a5268da ("pvh/dom0: whitelist PVH Dom0 ACPI tables")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 6378909b41
master date: 2025-03-26 12:32:03 +0100

xen/arch/x86/hvm/dom0_build.c

@@ -892,12 +892,20 @@ static bool __init pvh_acpi_table_allowed(const char *sig,
             return true;
         else
         {
+    skip:
             printk("Skipping table %.4s in non-ACPI non-reserved region\n",
                    sig);
             return false;
         }
     }
 
+    if ( !strncmp(sig, "OEM", 3) )
+    {
+        if ( acpi_memory_banned(address, size) )
+            goto skip;
+        return true;
+    }
+
     return false;
 }