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From:   Ilya Leoshkevich <iii@linux.ibm.com>
To:     Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Sven Schnelle <svens@linux.ibm.com>, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jens Freimann <jfreimann@redhat.com>,
        Ilya Leoshkevich <iii@linux.ibm.com>
Subject: [PATCH v2 2/6] KVM: s390: interrupt: Fix single-stepping into program interrupt handlers
Date:   Fri, 21 Jul 2023 13:57:55 +0200
Message-ID: <20230721120046.2262291-3-iii@linux.ibm.com>
In-Reply-To: <20230721120046.2262291-1-iii@linux.ibm.com>
References: <20230721120046.2262291-1-iii@linux.ibm.com>
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Currently, after single-stepping an instruction that generates a
specification exception, GDB ends up on the instruction immediately
following it.

The reason is that vcpu_post_run() injects the interrupt and sets
KVM_GUESTDBG_EXIT_PENDING, causing a KVM_SINGLESTEP exit. The
interrupt is not delivered, however, therefore userspace sees the
address of the next instruction.

Fix by letting the __vcpu_run() loop go into the next iteration,
where vcpu_pre_run() delivers the interrupt and sets
KVM_GUESTDBG_EXIT_PENDING.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/kvm/intercept.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index 954d39adf85c..7cdd927541b0 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -226,7 +226,22 @@ static int handle_itdb(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
-#define per_event(vcpu) (vcpu->arch.sie_block->iprcc & PGM_PER)
+static bool should_handle_per_event(const struct kvm_vcpu *vcpu)
+{
+	if (!guestdbg_enabled(vcpu))
+		return false;
+	if (!(vcpu->arch.sie_block->iprcc & PGM_PER))
+		return false;
+	if (guestdbg_sstep_enabled(vcpu) &&
+	    vcpu->arch.sie_block->iprcc != PGM_PER) {
+		/*
+		 * __vcpu_run() will exit after delivering the concurrently
+		 * indicated condition.
+		 */
+		return false;
+	}
+	return true;
+}
 
 static int handle_prog(struct kvm_vcpu *vcpu)
 {
@@ -242,7 +257,7 @@ static int handle_prog(struct kvm_vcpu *vcpu)
 	if (kvm_s390_pv_cpu_is_protected(vcpu))
 		return -EOPNOTSUPP;
 
-	if (guestdbg_enabled(vcpu) && per_event(vcpu)) {
+	if (should_handle_per_event(vcpu)) {
 		rc = kvm_s390_handle_per_event(vcpu);
 		if (rc)
 			return rc;
-- 
2.41.0