diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1ee2f42e74..5f31ca08fe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
  - On x86:
    - Restrict the cache flushing done as a result of guest physical memory map
      manipulations and memory type changes.
+   - Allow controlling the MTRR cache attribute of the Xen platform PCI device
+     BAR for HVM guests, to improve performance of guests using it to map the
+     grant table or foreign memory.
 
 ### Added
  - On x86:
diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
index 075e89e6d2..1d122982c6 100644
--- a/docs/man/xl.cfg.5.pod.in
+++ b/docs/man/xl.cfg.5.pod.in
@@ -2351,6 +2351,14 @@ Windows L<https://xenproject.org/windows-pv-drivers/>.
 Setting B<xen_platform_pci=0> with the default device_model "qemu-xen"
 requires at least QEMU 1.6.
 
+
+=item B<xen_platform_pci_bar_uc=BOOLEAN>
+
+B<x86 only:> Select whether the memory BAR of the Xen platform PCI device
+should have uncacheable (UC) cache attribute set in MTRR.
+
+Default is B<true>.
+
 =item B<viridian=[ "GROUP", "GROUP", ...]> or B<viridian=BOOLEAN>
 
 The groups of Microsoft Hyper-V (AKA viridian) compatible enlightenments
diff --git a/docs/misc/xenstore-paths.pandoc b/docs/misc/xenstore-paths.pandoc
index 01a340fafc..4994194e2b 100644
--- a/docs/misc/xenstore-paths.pandoc
+++ b/docs/misc/xenstore-paths.pandoc
@@ -234,6 +234,11 @@ These xenstore values are used to override some of the default string
 values in the SMBIOS table constructed in hvmloader. See the SMBIOS
 table specification at http://www.dmtf.org/standards/smbios/ 
 
+#### ~/hvmloader/pci/xen-platform-pci-bar-uc = ("1"|"0") [HVM,INTERNAL]
+
+Select whether the Xen platform PCI device MMIO BAR will have the uncacheable
+cache attribute set in the MTRRs by hvmloader.
+
 #### ~/bios-strings/oem-* = STRING [HVM,INTERNAL]
 
 1 to 99 OEM strings can be set in xenstore using values of the form
diff --git a/tools/firmware/hvmloader/config.h b/tools/firmware/hvmloader/config.h
index 6e1da137d7..c159db30ee 100644
--- a/tools/firmware/hvmloader/config.h
+++ b/tools/firmware/hvmloader/config.h
@@ -58,7 +58,7 @@ extern uint32_t *cpu_to_apicid;
 #define ACPI_TIS_HDR_ADDRESS 0xFED40F00UL
 
 extern uint32_t pci_mem_start;
-extern const uint32_t pci_mem_end;
+extern uint32_t pci_mem_end;
 extern uint64_t pci_hi_mem_start, pci_hi_mem_end;
 
 extern bool acpi_enabled;
diff --git a/tools/firmware/hvmloader/pci.c b/tools/firmware/hvmloader/pci.c
index cc67b18c03..c41c8d946a 100644
--- a/tools/firmware/hvmloader/pci.c
+++ b/tools/firmware/hvmloader/pci.c
@@ -29,8 +29,10 @@
 #include <xen/hvm/hvm_xs_strings.h>
 #include <xen/hvm/e820.h>
 
+#define PCI_VENDOR_ID_XEN       0x5853
+
 uint32_t pci_mem_start = HVM_BELOW_4G_MMIO_START;
-const uint32_t pci_mem_end = RESERVED_MEMBASE;
+uint32_t pci_mem_end = RESERVED_MEMBASE;
 uint64_t pci_hi_mem_start = 0, pci_hi_mem_end = 0;
 
 /*
@@ -116,6 +118,8 @@ void pci_setup(void)
      * experience the memory relocation bug described below.
      */
     bool allow_memory_relocate = 1;
+    /* Select the MTRR cache attribute of the xen platform pci device BAR. */
+    bool xenpci_bar_uc = true;
 
     BUILD_BUG_ON((typeof(*pci_devfn_decode_type))PCI_COMMAND_IO !=
                  PCI_COMMAND_IO);
@@ -130,6 +134,12 @@ void pci_setup(void)
     printf("Relocating guest memory for lowmem MMIO space %s\n",
            allow_memory_relocate?"enabled":"disabled");
 
+    s = xenstore_read(HVM_XS_XEN_PLATFORM_PCI_BAR_UC, NULL);
+    if ( s )
+        xenpci_bar_uc = strtoll(s, NULL, 0);
+    printf("Xen platform PCI device BAR MTRR cache attribute set to %s\n",
+           xenpci_bar_uc ? "UC" : "WB");
+
     s = xenstore_read("platform/mmio_hole_size", NULL);
     if ( s )
         mmio_hole_size = strtoll(s, NULL, 0);
@@ -271,6 +281,44 @@ void pci_setup(void)
             if ( bar_sz == 0 )
                 continue;
 
+            if ( !xenpci_bar_uc &&
+                 ((bar_data & PCI_BASE_ADDRESS_SPACE) ==
+                   PCI_BASE_ADDRESS_SPACE_MEMORY) &&
+                 vendor_id == PCI_VENDOR_ID_XEN &&
+                 (device_id == 0x0001 || device_id == 0x0002) )
+            {
+                if ( is_64bar )
+                {
+                     printf("xen platform pci dev %02x:%x unexpected MMIO 64bit BAR%u\n",
+                            devfn >> 3, devfn & 7, bar);
+                     goto skip_xenpci;
+                }
+
+                if ( bar_sz > pci_mem_end ||
+                     ((pci_mem_end - bar_sz) & ~(bar_sz - 1)) < pci_mem_start )
+                {
+                     printf("xen platform pci dev %02x:%x BAR%u size %llx overflows low PCI hole\n",
+                            devfn >> 3, devfn & 7, bar, bar_sz);
+                     goto skip_xenpci;
+                }
+
+                /* Put unconditionally at the end of the low PCI MMIO hole. */
+                pci_mem_end -= bar_sz;
+                pci_mem_end &= ~(bar_sz - 1);
+                bar_data &= ~PCI_BASE_ADDRESS_MEM_MASK;
+                bar_data |= pci_mem_end;
+                pci_writel(devfn, bar_reg, bar_data);
+                pci_devfn_decode_type[devfn] |= PCI_COMMAND_MEMORY;
+
+                /* Prefix BAR address with a 0 to match format used below. */
+                printf("pci dev %02x:%x bar %02x size "PRIllx": 0%08x\n",
+                       devfn >> 3, devfn & 7, bar_reg,
+                       PRIllx_arg(bar_sz), bar_data);
+
+                continue;
+            }
+ skip_xenpci:
+
             for ( i = 0; i < nr_bars; i++ )
                 if ( bars[i].bar_sz < bar_sz )
                     break;
@@ -310,7 +358,7 @@ void pci_setup(void)
         }
 
         /* Enable bus master for this function later */
-        pci_devfn_decode_type[devfn] = PCI_COMMAND_MASTER;
+        pci_devfn_decode_type[devfn] |= PCI_COMMAND_MASTER;
     }
 
     if ( mmio_hole_size )
diff --git a/tools/firmware/hvmloader/util.c b/tools/firmware/hvmloader/util.c
index 79c0e6bd4a..31b4411db7 100644
--- a/tools/firmware/hvmloader/util.c
+++ b/tools/firmware/hvmloader/util.c
@@ -867,7 +867,7 @@ void hvmloader_acpi_build_tables(struct acpi_config *config,
         config->table_flags |= ACPI_HAS_HPET;
 
     config->pci_start = pci_mem_start;
-    config->pci_len = pci_mem_end - pci_mem_start;
+    config->pci_len = RESERVED_MEMBASE - pci_mem_start;
     if ( pci_hi_mem_end > pci_hi_mem_start )
     {
         config->pci_hi_start = pci_hi_mem_start;
diff --git a/tools/include/libxl.h b/tools/include/libxl.h
index 24c81cf145..a8704e0268 100644
--- a/tools/include/libxl.h
+++ b/tools/include/libxl.h
@@ -1510,6 +1510,15 @@ void libxl_mac_copy(libxl_ctx *ctx, libxl_mac *dst, const libxl_mac *src);
  */
 #define LIBXL_HAVE_CREATEINFO_XEND_SUSPEND_EVTCHN_COMPAT
 
+/*
+ * LIBXL_HAVE_XEN_PLATFORM_PCI_BAR_UC
+ *
+ * libxl_domain_build_info contains a boolean 'u.hvm.xen_platform_pci_bar_uc'
+ * field to signal whether the XenPCI device BAR should have UC cache attribute
+ * set in MTRR.
+ */
+#define LIBXL_HAVE_XEN_PLATFORM_PCI_BAR_UC
+
 typedef char **libxl_string_list;
 void libxl_string_list_dispose(libxl_string_list *sl);
 int libxl_string_list_length(const libxl_string_list *sl);
diff --git a/tools/libs/light/libxl_create.c b/tools/libs/light/libxl_create.c
index 625ce5b040..9525d22312 100644
--- a/tools/libs/light/libxl_create.c
+++ b/tools/libs/light/libxl_create.c
@@ -313,6 +313,7 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
         libxl_defbool_setdefault(&b_info->u.hvm.usb,                false);
         libxl_defbool_setdefault(&b_info->u.hvm.vkb_device,         true);
         libxl_defbool_setdefault(&b_info->u.hvm.xen_platform_pci,   true);
+        libxl_defbool_setdefault(&b_info->u.hvm.xen_platform_pci_bar_uc, true);
         libxl_defbool_setdefault(&b_info->u.hvm.pirq,               false);
 
         libxl_defbool_setdefault(&b_info->u.hvm.spice.enable, false);
diff --git a/tools/libs/light/libxl_dom.c b/tools/libs/light/libxl_dom.c
index 4d67b0d282..a61085ca3b 100644
--- a/tools/libs/light/libxl_dom.c
+++ b/tools/libs/light/libxl_dom.c
@@ -819,6 +819,15 @@ static int hvm_build_set_xs_values(libxl__gc *gc,
             goto err;
     }
 
+    if (info->type == LIBXL_DOMAIN_TYPE_HVM) {
+        path = GCSPRINTF("/local/domain/%d/" HVM_XS_XEN_PLATFORM_PCI_BAR_UC,
+                         domid);
+        ret = libxl__xs_printf(gc, XBT_NULL, path, "%d",
+            libxl_defbool_val(info->u.hvm.xen_platform_pci_bar_uc));
+        if (ret)
+            goto err;
+    }
+
     return 0;
 
 err:
diff --git a/tools/libs/light/libxl_types.idl b/tools/libs/light/libxl_types.idl
index 57ae16ae78..a3a79d12b2 100644
--- a/tools/libs/light/libxl_types.idl
+++ b/tools/libs/light/libxl_types.idl
@@ -691,6 +691,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
                                        ("vkb_device",       libxl_defbool),
                                        ("soundhw",          string),
                                        ("xen_platform_pci", libxl_defbool),
+                                       ("xen_platform_pci_bar_uc", libxl_defbool),
                                        ("usbdevice_list",   libxl_string_list),
                                        ("vendor_device",    libxl_vendor_device),
                                        # See libxl_ms_vm_genid_generate()
diff --git a/tools/xl/xl_parse.c b/tools/xl/xl_parse.c
index 98b3612d0f..7e11c62ba0 100644
--- a/tools/xl/xl_parse.c
+++ b/tools/xl/xl_parse.c
@@ -2917,6 +2917,8 @@ skip_usbdev:
         xlu_cfg_replace_string (config, "soundhw", &b_info->u.hvm.soundhw, 0);
         xlu_cfg_get_defbool(config, "xen_platform_pci",
                             &b_info->u.hvm.xen_platform_pci, 0);
+        xlu_cfg_get_defbool(config, "xen_platform_pci_bar_uc",
+                            &b_info->u.hvm.xen_platform_pci_bar_uc, 0);
 
         if(b_info->u.hvm.vnc.listen
            && b_info->u.hvm.vnc.display
diff --git a/xen/include/public/hvm/hvm_xs_strings.h b/xen/include/public/hvm/hvm_xs_strings.h
index e1ed078628..e977d5a8b1 100644
--- a/xen/include/public/hvm/hvm_xs_strings.h
+++ b/xen/include/public/hvm/hvm_xs_strings.h
@@ -14,6 +14,8 @@
 #define HVM_XS_BIOS                    "hvmloader/bios"
 #define HVM_XS_GENERATION_ID_ADDRESS   "hvmloader/generation-id-address"
 #define HVM_XS_ALLOW_MEMORY_RELOCATE   "hvmloader/allow-memory-relocate"
+/* Set Xen platform pci device BAR as UC in MTRR */
+#define HVM_XS_XEN_PLATFORM_PCI_BAR_UC "hvmloader/pci/xen-platform-pci-bar-uc"
 
 /* The following values allow additional ACPI tables to be added to the
  * virtual ACPI BIOS that hvmloader constructs. The values specify the guest