From: Mukesh R <[email protected]> Sent: Tuesday, February 17, 2026
3:12 PM
>
> MSVC compiler, used to compile the Microsoft Hyper-V hypervisor currently,
> has an assert intrinsic that uses interrupt vector 0x29 to create an
> exception. This will cause hypervisor to then crash and collect core. As
> such, if this interrupt number is assigned to a device by Linux and the
> device generates it, hypervisor will crash. There are two other such
> vectors hard coded in the hypervisor, 0x2C and 0x2D for debug purposes.
> Fortunately, the three vectors are part of the kernel driver space and
> that makes it feasible to reserve them early so they are not assigned
> later.
>
> Signed-off-by: Mukesh Rathor <[email protected]>
> ---
>
> v1: Add ifndef CONFIG_X86_FRED (thanks hpa)
> v2: replace ifndef with cpu_feature_enabled() (thanks hpa and tglx)
>
> arch/x86/kernel/cpu/mshyperv.c | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 579fb2c64cfd..88ca127dc6d4 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -478,6 +478,28 @@ int hv_get_hypervisor_version(union
> hv_hypervisor_version_info *info)
> }
> EXPORT_SYMBOL_GPL(hv_get_hypervisor_version);
>
> +/*
> + * Reserve vectors hard coded in the hypervisor. If used outside, the
> hypervisor
> + * will either crash or hang or attempt to break into debugger.
> + */
> +static void hv_reserve_irq_vectors(void)
> +{
> + #define HYPERV_DBG_FASTFAIL_VECTOR 0x29
> + #define HYPERV_DBG_ASSERT_VECTOR 0x2C
> + #define HYPERV_DBG_SERVICE_VECTOR 0x2D
> +
> + if (cpu_feature_enabled(X86_FEATURE_FRED))
> + return;
> +
> + if (test_and_set_bit(HYPERV_DBG_ASSERT_VECTOR, system_vectors) ||
> + test_and_set_bit(HYPERV_DBG_SERVICE_VECTOR, system_vectors) ||
> + test_and_set_bit(HYPERV_DBG_FASTFAIL_VECTOR, system_vectors))
> + BUG();
> +
> + pr_info("Hyper-V:reserve vectors: %d %d %d\n", HYPERV_DBG_ASSERT_VECTOR,
> + HYPERV_DBG_SERVICE_VECTOR, HYPERV_DBG_FASTFAIL_VECTOR);
I'm a little late to the party here, but I've always seen Intel interrupt
vectors
displayed as 2-digit hex numbers. This info message is displaying decimal,
which is atypical and will probably be confusing.
Michael
> +}
> +
> static void __init ms_hyperv_init_platform(void)
> {
> int hv_max_functions_eax, eax;
> @@ -510,6 +532,11 @@ static void __init ms_hyperv_init_platform(void)
>
> hv_identify_partition_type();
>
> +#ifndef CONFIG_X86_FRED
> + if (hv_root_partition())
> + hv_reserve_irq_vectors();
> +#endif /* CONFIG_X86_FRED */
> +
> if (cc_platform_has(CC_ATTR_SNP_SECURE_AVIC))
> ms_hyperv.hints |= HV_DEPRECATING_AEOI_RECOMMENDED;
>
> --
> 2.51.2.vfs.0.1
>
