[PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[Mukesh R]

From: Mukesh Rathor <mrathor@linux.microsoft.com>

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 <mrathor@linux.microsoft.com>
---

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);
+}
+
 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

Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[Wei Liu]

On Tue, Feb 17, 2026 at 03:11:58PM -0800, Mukesh R wrote:
> From: Mukesh Rathor <mrathor@linux.microsoft.com>
> 
> 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 <mrathor@linux.microsoft.com>

Queued. I also did a few cosmetic changes to this patch.

Wei

Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[Wei Liu]

On Tue, Feb 17, 2026 at 03:11:58PM -0800, Mukesh R wrote:
> From: Mukesh Rathor <mrathor@linux.microsoft.com>
> 
> 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 <mrathor@linux.microsoft.com>
> ---
> 
> 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);
> +}
> +
>  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 */
> +

On a CONFIG_X86_FRED=y system, this call is skipped. However, the kernel
may not have FRED active, so the vectors should still be reserved.

I think the function should always be called.

Wei

>  	if (cc_platform_has(CC_ATTR_SNP_SECURE_AVIC))
>  		ms_hyperv.hints |= HV_DEPRECATING_AEOI_RECOMMENDED;
>  
> -- 
> 2.51.2.vfs.0.1
> 
> 

Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[kernel test robot]

Hi Mukesh,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/x86/core]
[also build test WARNING on linus/master v6.19 next-20260217]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Mukesh-R/x86-hyperv-Reserve-3-interrupt-vectors-used-exclusively-by-mshv/20260218-071406
base:   tip/x86/core
patch link:    https://lore.kernel.org/r/20260217231158.1184736-1-mrathor%40linux.microsoft.com
patch subject: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv
config: x86_64-rhel-9.4-ltp (https://download.01.org/0day-ci/archive/20260218/202602180851.Pi2PY5LX-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260218/202602180851.Pi2PY5LX-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202602180851.Pi2PY5LX-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> arch/x86/kernel/cpu/mshyperv.c:485:13: warning: 'hv_reserve_irq_vectors' defined but not used [-Wunused-function]
     485 | static void hv_reserve_irq_vectors(void)
         |             ^~~~~~~~~~~~~~~~~~~~~~


vim +/hv_reserve_irq_vectors +485 arch/x86/kernel/cpu/mshyperv.c

   480	
   481	/*
   482	 * Reserve vectors hard coded in the hypervisor. If used outside, the hypervisor
   483	 * will either crash or hang or attempt to break into debugger.
   484	 */
 > 485	static void hv_reserve_irq_vectors(void)
   486	{
   487		#define HYPERV_DBG_FASTFAIL_VECTOR	0x29
   488		#define HYPERV_DBG_ASSERT_VECTOR	0x2C
   489		#define HYPERV_DBG_SERVICE_VECTOR	0x2D
   490	
   491		if (cpu_feature_enabled(X86_FEATURE_FRED))
   492			return;
   493	
   494		if (test_and_set_bit(HYPERV_DBG_ASSERT_VECTOR, system_vectors) ||
   495		    test_and_set_bit(HYPERV_DBG_SERVICE_VECTOR, system_vectors) ||
   496		    test_and_set_bit(HYPERV_DBG_FASTFAIL_VECTOR, system_vectors))
   497			BUG();
   498	
   499		pr_info("Hyper-V:reserve vectors: %d %d %d\n", HYPERV_DBG_ASSERT_VECTOR,
   500			HYPERV_DBG_SERVICE_VECTOR, HYPERV_DBG_FASTFAIL_VECTOR);
   501	}
   502	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[kernel test robot]

Hi Mukesh,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/x86/core]
[also build test WARNING on linus/master v6.19 next-20260217]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Mukesh-R/x86-hyperv-Reserve-3-interrupt-vectors-used-exclusively-by-mshv/20260218-071406
base:   tip/x86/core
patch link:    https://lore.kernel.org/r/20260217231158.1184736-1-mrathor%40linux.microsoft.com
patch subject: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv
config: x86_64-rhel-9.4 (https://download.01.org/0day-ci/archive/20260218/202602182000.O5dSFVVd-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260218/202602182000.O5dSFVVd-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202602182000.O5dSFVVd-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> arch/x86/kernel/cpu/mshyperv.c:485:13: warning: 'hv_reserve_irq_vectors' defined but not used [-Wunused-function]
     485 | static void hv_reserve_irq_vectors(void)
         |             ^~~~~~~~~~~~~~~~~~~~~~


vim +/hv_reserve_irq_vectors +485 arch/x86/kernel/cpu/mshyperv.c

   480	
   481	/*
   482	 * Reserve vectors hard coded in the hypervisor. If used outside, the hypervisor
   483	 * will either crash or hang or attempt to break into debugger.
   484	 */
 > 485	static void hv_reserve_irq_vectors(void)
   486	{
   487		#define HYPERV_DBG_FASTFAIL_VECTOR	0x29
   488		#define HYPERV_DBG_ASSERT_VECTOR	0x2C
   489		#define HYPERV_DBG_SERVICE_VECTOR	0x2D
   490	
   491		if (cpu_feature_enabled(X86_FEATURE_FRED))
   492			return;
   493	
   494		if (test_and_set_bit(HYPERV_DBG_ASSERT_VECTOR, system_vectors) ||
   495		    test_and_set_bit(HYPERV_DBG_SERVICE_VECTOR, system_vectors) ||
   496		    test_and_set_bit(HYPERV_DBG_FASTFAIL_VECTOR, system_vectors))
   497			BUG();
   498	
   499		pr_info("Hyper-V:reserve vectors: %d %d %d\n", HYPERV_DBG_ASSERT_VECTOR,
   500			HYPERV_DBG_SERVICE_VECTOR, HYPERV_DBG_FASTFAIL_VECTOR);
   501	}
   502	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

RE: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[Michael Kelley]

From: Mukesh R <mrathor@linux.microsoft.com> 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 <mrathor@linux.microsoft.com>
> ---
> 
> 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
> 

Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[Wei Liu]

On Fri, Feb 20, 2026 at 05:14:26PM +0000, Michael Kelley wrote:
> From: Mukesh R <mrathor@linux.microsoft.com> 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 <mrathor@linux.microsoft.com>
> > ---
> > 
> > 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.

Noted. The pull request to Linus has been sent. We will change the
format in a follow up patch.

Wei

Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[Mukesh R]

On 2/20/26 10:45, Wei Liu wrote:
> On Fri, Feb 20, 2026 at 05:14:26PM +0000, Michael Kelley wrote:
>> From: Mukesh R <mrathor@linux.microsoft.com> 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 <mrathor@linux.microsoft.com>
>>> ---
>>>
>>> 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.
> 
> Noted. The pull request to Linus has been sent. We will change the
> format in a follow up patch.

Well, there is no 0x prefix, so should not be confusing, but no big
deal, whatever.....

Thanks,
-Mukesh

Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv

[Wei Liu]

On Fri, Feb 20, 2026 at 10:56:07AM -0800, Mukesh R wrote:
> On 2/20/26 10:45, Wei Liu wrote:
> > On Fri, Feb 20, 2026 at 05:14:26PM +0000, Michael Kelley wrote:
> > > From: Mukesh R <mrathor@linux.microsoft.com> 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 <mrathor@linux.microsoft.com>
> > > > ---
> > > > 
> > > > 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.
> > 
> > Noted. The pull request to Linus has been sent. We will change the
> > format in a follow up patch.
> 
> Well, there is no 0x prefix, so should not be confusing, but no big
> deal, whatever.....
> 

When I change these I will add the 0x prefix as well.

Wei

> Thanks,
> -Mukesh
> 
> 
>