Re: [PATCH v2] x86/hyperv: Reserve 3 interrupt vectors used exclusively by mshv
From: Mukesh R
Date: Fri Feb 20 2026 - 13:56:30 EST
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@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx>
---
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