Commit 0719881b authored by Dexuan Cui's avatar Dexuan Cui Committed by Wei Liu
Browse files

x86/hyperv: Fix serial console interrupts for fully enlightened TDX guests 



When a fully enlightened TDX guest runs on Hyper-V, the UEFI firmware sets
the HW_REDUCED flag and consequently ttyS0 interrupts can't work. Fix the
issue by overriding x86_init.acpi.reduced_hw_early_init().

Reviewed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Reviewed-by: default avatarTianyu Lan <tiala@microsoft.com>
Signed-off-by: default avatarDexuan Cui <decui@microsoft.com>
Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230824080712.30327-5-decui@microsoft.com
parent 68f2f2bc

arch/x86/kernel/cpu/mshyperv.c

+22 −0
Original line number Diff line number Diff line
@@ -323,6 +323,26 @@ static void __init hv_smp_prepare_cpus(unsigned int max_cpus) 
}

#endif



/*

 * When a fully enlightened TDX VM runs on Hyper-V, the firmware sets the

 * HW_REDUCED flag: refer to acpi_tb_create_local_fadt(). Consequently ttyS0

 * interrupts can't work because request_irq() -> ... -> irq_to_desc() returns

 * NULL for ttyS0. This happens because mp_config_acpi_legacy_irqs() sees a

 * nr_legacy_irqs() of 0, so it doesn't initialize the array 'mp_irqs[]', and

 * later setup_IO_APIC_irqs() -> find_irq_entry() fails to find the legacy irqs

 * from the array and hence doesn't create the necessary irq description info.

 *

 * Clone arch/x86/kernel/acpi/boot.c: acpi_generic_reduced_hw_init() here,

 * except don't change 'legacy_pic', which keeps its default value

 * 'default_legacy_pic'. This way, mp_config_acpi_legacy_irqs() sees a non-zero

 * nr_legacy_irqs() and eventually serial console interrupts works properly.

 */

static void __init reduced_hw_init(void)

{

	x86_init.timers.timer_init	= x86_init_noop;

	x86_init.irqs.pre_vector_init	= x86_init_noop;

}



static void __init ms_hyperv_init_platform(void)

{

	int hv_max_functions_eax;
@@ -433,6 +453,8 @@ static void __init ms_hyperv_init_platform(void) 


				/* Don't trust Hyper-V's TLB-flushing hypercalls. */

				ms_hyperv.hints &= ~HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED;



				x86_init.acpi.reduced_hw_early_init = reduced_hw_init;

			}

		}

	}