[PATCH] Add support for ESRT loading under Xen

[Demi Marie Obenour <demi@invisiblethingslab.com>]

This is needed for fwupd to work in Qubes OS.

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
---
 drivers/firmware/efi/esrt.c | 34 ++++++++++++++++++++++++----------
 drivers/xen/efi.c           | 33 +++++++++++++++++++++++++++++++++
 include/linux/efi.h         | 10 ++++++++++
 3 files changed, 67 insertions(+), 10 deletions(-)

diff --git a/drivers/firmware/efi/esrt.c b/drivers/firmware/efi/esrt.c
index 2a2f52b017e736dd995c69e8aeb5fbd7761732e5..c0fc149a838044cc16bb08a374a0c8ea6b7dcbff 100644
--- a/drivers/firmware/efi/esrt.c
+++ b/drivers/firmware/efi/esrt.c
@@ -244,22 +244,36 @@ void __init efi_esrt_init(void)
 	struct efi_system_resource_table tmpesrt;
 	size_t size, max, entry_size, entries_size;
 	efi_memory_desc_t md;
-	int rc;
 	phys_addr_t end;
 
-	if (!efi_enabled(EFI_MEMMAP))
-		return;
-
 	pr_debug("esrt-init: loading.\n");
 	if (!esrt_table_exists())
 		return;
 
-	rc = efi_mem_desc_lookup(efi.esrt, &md);
-	if (rc < 0 ||
-	    (!(md.attribute & EFI_MEMORY_RUNTIME) &&
-	     md.type != EFI_BOOT_SERVICES_DATA &&
-	     md.type != EFI_RUNTIME_SERVICES_DATA)) {
-		pr_warn("ESRT header is not in the memory map.\n");
+	if (efi_enabled(EFI_MEMMAP)) {
+		if (efi_mem_desc_lookup(efi.esrt, &md) < 0 ||
+		    (!(md.attribute & EFI_MEMORY_RUNTIME) &&
+		     md.type != EFI_BOOT_SERVICES_DATA &&
+		     md.type != EFI_RUNTIME_SERVICES_DATA)) {
+			pr_warn("ESRT header is not in the memory map.\n");
+			return;
+		}
+	} else if (IS_ENABLED(CONFIG_XEN_EFI) && efi_enabled(EFI_PARAVIRT)) {
+		if (!xen_efi_mem_desc_lookup(efi.esrt, &md)) {
+			pr_warn("Failed to lookup ESRT header in Xen memory map\n");
+			return;
+		}
+
+		/* Recent Xen versions relocate the ESRT to memory of type
+		 * EfiRuntimeServicesData, which Xen will not reuse.  If the ESRT
+		 * is not in EfiRuntimeServicesData memory, it has not been reserved
+		 * by Xen and might be allocated to other guests, so it cannot
+		 * safely be used. */
+		if (md.type != EFI_RUNTIME_SERVICES_DATA) {
+			pr_warn("Xen did not reserve ESRT, ignoring it\n");
+			return;
+		}
+	} else {
 		return;
 	}
 
diff --git a/drivers/xen/efi.c b/drivers/xen/efi.c
index d1ff2186ebb48a7c0981ecb6d4afcbbb25ffcea0..b313f213822f0fd5ba6448f6f6f453cfda4c7e23 100644
--- a/drivers/xen/efi.c
+++ b/drivers/xen/efi.c
@@ -26,6 +26,7 @@
 
 #include <xen/interface/xen.h>
 #include <xen/interface/platform.h>
+#include <xen/page.h>
 #include <xen/xen.h>
 #include <xen/xen-ops.h>
 
@@ -40,6 +41,38 @@
 
 #define efi_data(op)	(op.u.efi_runtime_call)
 
+static_assert(XEN_PAGE_SHIFT == EFI_PAGE_SHIFT,
+              "Mismatch between EFI_PAGE_SHIFT and XEN_PAGE_SHIFT");
+
+bool xen_efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *md)
+{
+	struct xen_platform_op op = {
+		.cmd = XENPF_firmware_info,
+		.u.firmware_info = {
+			.type = XEN_FW_EFI_INFO,
+			.index = XEN_FW_EFI_MEM_INFO,
+			.u.efi_info.mem.addr = phys_addr,
+			.u.efi_info.mem.size = ((u64)-1ULL) - phys_addr,
+		}
+	};
+	union xenpf_efi_info *info = &op.u.firmware_info.u.efi_info;
+	int rc;
+
+	memset(md, 0, sizeof(*md)); /* initialize md even on failure */
+	rc = HYPERVISOR_platform_op(&op);
+	if (rc) {
+		pr_warn("Could not obtain information on address %llu from Xen: "
+			"error %d\n", phys_addr, rc);
+		return false;
+	}
+
+	md->attribute = info->mem.attr;
+	md->type = info->mem.type;
+	md->num_pages = info->mem.size >> XEN_PAGE_SHIFT;
+	md->phys_addr = info->mem.addr;
+	return true;
+}
+
 static efi_status_t xen_efi_get_time(efi_time_t *tm, efi_time_cap_t *tc)
 {
 	struct xen_platform_op op = INIT_EFI_OP(get_time);
diff --git a/include/linux/efi.h b/include/linux/efi.h
index d2b84c2fec39f0268324d1a38a73ed67786973c9..0598869cdc924aef0e2b9cacc4450b728e1a98c7 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1327,1 +1327,11 @@ struct linux_efi_coco_secret_area {
+#if IS_ENABLED(CONFIG_XEN_EFI)
+extern bool xen_efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md);
+#else
+static inline bool xen_efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
+{
+	BUILD_BUG();
+	return false;
+}
+#endif
+
 #endif /* _LINUX_EFI_H */
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab