linux-kernel - Re: [RFC][PATCH v0] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

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Message-ID: <877bu0au1t.fsf@redhat.com>
Date: Fri, 02 Jan 2026 16:55:10 +0100
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Mukesh Rathor <mrathor@...ux.microsoft.com>,
 linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com, longli@...rosoft.com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
 x86@...nel.org, hpa@...or.com
Subject: Re: [RFC][PATCH v0] x86/hyperv: Reserve 3 interrupt vectors used
 exclusively by mshv

Mukesh Rathor <mrathor@...ux.microsoft.com> writes:

> 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. 
>
> 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 <mrathor@...ux.microsoft.com>
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 579fb2c64cfd..19d41f7434df 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -478,6 +478,25 @@ 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 crash or hang or 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 (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();

Would it be less hackish to use sysvec_install() with a dummy handler
for all three vectors instead? 

> +
> +	pr_info("Hyper-V:reserve vectors: %d %d %d\n", HYPERV_DBG_ASSERT_VECTOR,
> +		HYPERV_DBG_SERVICE_VECTOR, HYPERV_DBG_FASTFAIL_VECTOR);
> +}
> +
>  static void __init ms_hyperv_init_platform(void)
>  {
>  	int hv_max_functions_eax, eax;
> @@ -510,6 +529,9 @@ static void __init ms_hyperv_init_platform(void)
>  
>  	hv_identify_partition_type();
>  
> +	if (hv_root_partition())
> +		hv_reserve_irq_vectors();
> +
>  	if (cc_platform_has(CC_ATTR_SNP_SECURE_AVIC))
>  		ms_hyperv.hints |= HV_DEPRECATING_AEOI_RECOMMENDED;

-- 
Vitaly