x86/hyperv/vtl: Setup the 64-bit trampoline for TDX guests

The hypervisor is an untrusted entity for TDX guests. It cannot be used
to boot secondary CPUs - neither via hypercalls nor the INIT assert,
de-assert, plus Start-Up IPI messages.

Instead, the platform virtual firmware boots the secondary CPUs and
puts them in a state to transfer control to the kernel. This mechanism uses
the wakeup mailbox described in the Multiprocessor Wakeup Structure of the
ACPI specification. The entry point to the kernel is trampoline_start64.

Allocate and setup the trampoline using the default x86_platform callbacks.

The platform firmware configures the secondary CPUs in long mode. It is no
longer necessary to locate the trampoline under 1MB memory. After handoff
from firmware, the trampoline code switches briefly to 32-bit addressing
mode, which has an addressing limit of 4GB. Set the upper bound of the
trampoline memory accordingly.

Reviewed-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Dexuan Cui <dexuan@kernel.org>

diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index e045bf3a2c5947f85bc5368721d7d879868b1c7e..b94fffa67312856e2c97251182a6dcd464456c30 100644 (file)
--- a/arch/x86/hyperv/hv_vtl.c
+++ b/arch/x86/hyperv/hv_vtl.c
@@ -68,9 +68,14 @@ void __init hv_vtl_init_platform(void)
         */
        pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);
 
-       x86_platform.realmode_reserve = x86_init_noop;
-       x86_platform.realmode_init = x86_init_noop;
-       real_mode_header = &hv_vtl_real_mode_header;
+       /* There is no paravisor present if we are here. */
+       if (hv_isolation_type_tdx()) {
+               x86_init.resources.realmode_limit = SZ_4G;
+       } else {
+               x86_platform.realmode_reserve = x86_init_noop;
+               x86_platform.realmode_init = x86_init_noop;
+               real_mode_header = &hv_vtl_real_mode_header;
+       }
        x86_init.irqs.pre_vector_init = x86_init_noop;
        x86_init.timers.timer_init = x86_init_noop;
        x86_init.resources.probe_roms = x86_init_noop;