linux-kernel - [RFC PATCH v2 09/35] KVM: selftests: Add #VC exception handler with error code support

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Message-ID: <20250923050942.206116-10-Neeraj.Upadhyay@amd.com>
Date: Tue, 23 Sep 2025 10:39:16 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: <kvm@...r.kernel.org>, <seanjc@...gle.com>, <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <Thomas.Lendacky@....com>,
	<nikunj@....com>, <Santosh.Shukla@....com>, <Vasant.Hegde@....com>,
	<Suravee.Suthikulpanit@....com>, <bp@...en8.de>, <David.Kaplan@....com>,
	<huibo.wang@....com>, <naveen.rao@....com>, <pgonda@...gle.com>,
	<linux-kselftest@...r.kernel.org>, <shuah@...nel.org>, <tiala@...rosoft.com>
Subject: [RFC PATCH v2 09/35] KVM: selftests: Add #VC exception handler with error code support

The VMM Communication Exception (#VC, vector 29) pushes an error
code onto the stack, similar to exceptions like #PF or #GP.

The generic IDT handler generation macro in the selftests incorrectly
assumed that all vectors from 18 to 255 do not have an error code. For
new tests (added in subsequent commits) which trigger #VC exception,
this incorrect assumption caused the handler to misinterpret the stack
frame and the ex_regs fields, leading to stack corruption upon IRET.

Fix this by explicitly defining a handler for vector 29 that correctly
accounts for the error code.

This allows selftests to properly catch and handle #VC exceptions, which
is a prerequisite for testing features like SEV-ES.

Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
---
 tools/testing/selftests/kvm/lib/x86/handlers.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/lib/x86/handlers.S b/tools/testing/selftests/kvm/lib/x86/handlers.S
index 7629819734af..19715a58f5d2 100644
--- a/tools/testing/selftests/kvm/lib/x86/handlers.S
+++ b/tools/testing/selftests/kvm/lib/x86/handlers.S
@@ -76,6 +76,8 @@ idt_handler_code:
 	HANDLERS has_error=1 from=10 to=14
 	HANDLERS has_error=0 from=15 to=16
 	HANDLERS has_error=1 from=17 to=17
-	HANDLERS has_error=0 from=18 to=255
+	HANDLERS has_error=0 from=18 to=28
+	HANDLERS has_error=1 from=29 to=29
+	HANDLERS has_error=0 from=30 to=255

 .section        .note.GNU-stack, "", %progbits
-- 
2.34.1