[PATCH v3 49/49] hw/i386: Add support for loading BIOS using guest_memfd

[Michael Roth]

TODO: - Add proper handling for non-64K-aligned BIOS images.
      - Add proper handling for BIOS pflash area which should be
        initially mapped as shared, resulting in unecessary
        KVM_EXIT_MEMORY_FAULTs

When guest_memfd is enabled, the BIOS is generally part of the initial
encrypted guest image and will be accessed as private guest memory. Add
the necessary changes to set up the associated RAM region with a
guest_memfd backend to allow for this.

Current support centers around using -bios to load the BIOS data.
Support for loading the BIOS via pflash requires additional enablement
since those interfaces rely on the use of ROM memory regions which make
use of the KVM_MEM_READONLY memslot flag, which is not supported for
guest_memfd-backed memslots.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 hw/i386/x86.c | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index e3ddc39133..ea2d03cc02 100644
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -1147,10 +1147,18 @@ void x86_bios_rom_init(MachineState *ms, const char 
*default_firmware,
     }
     if (bios_size <= 0 ||
         (bios_size % 65536) != 0) {
-        goto bios_error;
+        g_warning("%s: Unaligned BIOS size %d", __func__, bios_size);
+        if (!machine_require_guest_memfd(ms)) {
+            goto bios_error;
+        }
     }
     bios = g_malloc(sizeof(*bios));
-    memory_region_init_ram(bios, NULL, "pc.bios", bios_size, &error_fatal);
+    if (machine_require_guest_memfd(ms)) {
+        memory_region_init_ram_guest_memfd(bios, NULL, "pc.bios", bios_size,
+                                           &error_fatal);
+    } else {
+        memory_region_init_ram(bios, NULL, "pc.bios", bios_size, &error_fatal);
+    }
     if (sev_enabled()) {
         /*
          * The concept of a "reset" simply doesn't exist for
@@ -1173,17 +1181,19 @@ void x86_bios_rom_init(MachineState *ms, const char 
*default_firmware,
     }
     g_free(filename);
 
-    /* map the last 128KB of the BIOS in ISA space */
-    isa_bios_size = MIN(bios_size, 128 * KiB);
-    isa_bios = g_malloc(sizeof(*isa_bios));
-    memory_region_init_alias(isa_bios, NULL, "isa-bios", bios,
-                             bios_size - isa_bios_size, isa_bios_size);
-    memory_region_add_subregion_overlap(rom_memory,
-                                        0x100000 - isa_bios_size,
-                                        isa_bios,
-                                        1);
-    if (!isapc_ram_fw) {
-        memory_region_set_readonly(isa_bios, true);
+    if (!machine_require_guest_memfd(ms)) {
+        /* map the last 128KB of the BIOS in ISA space */
+        isa_bios_size = MIN(bios_size, 128 * KiB);
+        isa_bios = g_malloc(sizeof(*isa_bios));
+        memory_region_init_alias(isa_bios, NULL, "isa-bios", bios,
+                                 bios_size - isa_bios_size, isa_bios_size);
+        memory_region_add_subregion_overlap(rom_memory,
+                                            0x100000 - isa_bios_size,
+                                            isa_bios,
+                                            1);
+        if (!isapc_ram_fw) {
+            memory_region_set_readonly(isa_bios, true);
+        }
     }
 
     /* map all the bios at the top of memory */
-- 
2.25.1