[PATCH v1 22/40] i386/tdx: Skip BIOS shadowing setup

Xiaoyao Li
2022-08-02T07:50:06Z

TDX doesn't support map different GPAs to same private memory. Thus,
aliasing top 128KB of BIOS as isa-bios is not supported.

On the other hand, TDX guest cannot go to real mode, it can work fine
without isa-bios.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
Changes from RFC v4:
- update commit message and comment to clarify
---
hw/i386/x86.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index 006b0e670e4d..a389ee26265a 100644
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -1172,17 +1172,20 @@ 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);
+ /* For TDX, alias different GPAs to same private memory is not supported */
+ if (!is_tdx_vm()) {
+ /* 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 */
--
2.27.0