x86/mcfg: relax memory map checks on newer firmware

Per PCI Firmware 3.3 specification, section 4.1.2, ECAM space must be
reserved by declaring a motherboard resource, but there's no requirement to
mention it in E820.  The specification additionally states that: the
resources can optionally be returned in Int15 E820h or EFIGetMemoryMap as
reserved memory.

Recent Lenovo systems have been found to have the MMCFG region in an
E820 hole, which looks to be technically spec compliant, but is rejected
by Xen.

The logic was introduced in Linux in 2006 as 946f2ee5c731 ("[PATCH]
i386/x86-64: Check that MCFG points to an e820 reserved area").  This was
picked up by Xen when MCFG support was added in 3b35911d70 ("Enable pci
mmcfg and ATS for x86_64").  Apply an approach similar to what Linux has
done in 199f968f1484 ("x86/pci: Skip early E820 check for ECAM region") and
relax the strict reserved region checking so it's only done for firmware
manufactured prior to 2016.  For firmware from 2016 and newer allow MCFG
region to reside in holes on the memory map.  Note Xen is still more strict
than Linux however, as it will refuse to use MCFG regions that overlap with
memory map regions different than reserved.

When dom0 boots it can prevent access to misconfigured MCFG regions by
using the PHYSDEVOP_pci_mmcfg_reserved hypercall.  This brings Xen's early
usage of MCFG (prior to ACPI AML parsing) more in line with the
implementation in Linux.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

xen/arch/x86/x86_64/mmconfig-shared.c

@@ -13,6 +13,7 @@
  */
 
 #include <xen/acpi.h>
+#include <xen/dmi.h>
 #include <xen/init.h>
 #include <xen/mm.h>
 #include <xen/param.h>
@@ -369,12 +370,15 @@ static bool __init pci_mmcfg_reject_broken(void)
     typeof(pci_mmcfg_config[0]) *cfg;
     int i;
     bool valid = true;
+    int year;
 
     if ((pci_mmcfg_config_num == 0) ||
         (pci_mmcfg_config == NULL) ||
         (pci_mmcfg_config[0].address == 0))
         return 0;
 
+    dmi_get_date(DMI_BIOS_DATE, &year, NULL, NULL);
+
     for (i = 0; i < pci_mmcfg_config_num; i++) {
         u64 addr, size;
 
@@ -390,7 +394,13 @@ static bool __init pci_mmcfg_reject_broken(void)
                (unsigned int)cfg->start_bus_number,
                (unsigned int)cfg->end_bus_number);
 
-        if ( !is_mmconf_reserved(addr, size, i, cfg) ||
+        /*
+         * For firmwares prior to 2016, confirm that MMCFG is marked as
+         * reserved.  For 2016 and later, also allow MMCFG being in a hole.
+         */
+        if ( ((year < 2016 || !is_memory_hole(maddr_to_mfn(addr),
+                                              maddr_to_mfn(addr + size - 1))) &&
+              !is_mmconf_reserved(addr, size, i, cfg)) ||
              pci_mmcfg_arch_enable(i) < 0 )
         {
             pci_mmcfg_arch_disable(i);