linux-kernel - [PATCH] KVM: PPC: Book3S HV: Fix IRQ map warnings with XICS on pSeries KVM Guest

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Message-ID: <20250425185641.1611857-1-amachhiw@linux.ibm.com>
Date: Sat, 26 Apr 2025 00:26:41 +0530
From: Amit Machhiwal <amachhiw@...ux.ibm.com>
To: Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Cc: Amit Machhiwal <amachhiw@...ux.ibm.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        Shivaprasad G Bhat <sbhat@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Naveen N Rao <naveen@...nel.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: PPC: Book3S HV: Fix IRQ map warnings with XICS on pSeries KVM Guest

The commit 9576730d0e6e ("KVM: PPC: select IRQ_BYPASS_MANAGER") enabled
IRQ_BYPASS_MANAGER when CONFIG_KVM was set. Subsequently, commit
c57875f5f9be ("KVM: PPC: Book3S HV: Enable IRQ bypass") enabled IRQ
bypass and added the necessary callbacks to create/remove the mappings
between host real IRQ and the guest GSI.

The availability of IRQ bypass is determined by the arch-specific
function kvm_arch_has_irq_bypass(), which invokes
kvmppc_irq_bypass_add_producer_hv(). This function, in turn, calls
kvmppc_set_passthru_irq_hv() to create a mapping in the passthrough IRQ
map, associating a host IRQ to a guest GSI.

However, when a pSeries KVM guest (L2) is booted within an LPAR (L1)
with the kernel boot parameter `xive=off`, it defaults to using emulated
XICS controller. As an attempt to establish host IRQ to guest GSI
mappings via kvmppc_set_passthru_irq() on a PCI device hotplug
(passhthrough) operation fail, returning -ENOENT. This failure occurs
because only interrupts with EOI operations handled through OPAL calls
(verified via is_pnv_opal_msi()) are currently supported.

These mapping failures lead to below repeated warnings in the L1 host:

 [  509.220349] kvmppc_set_passthru_irq_hv: Could not assign IRQ map for (58,4970)
 [  509.220368] kvmppc_set_passthru_irq (irq 58, gsi 4970) fails: -2
 [  509.220376] vfio-pci 0015:01:00.0: irq bypass producer (token 0000000090bc635b) registration fails: -2
 ...
 [  509.291781] vfio-pci 0015:01:00.0: irq bypass producer (token 000000003822eed8) registration fails: -2

Fix this by restricting IRQ bypass enablement on pSeries systems by
making the IRQ bypass callbacks unavailable when running on pSeries
platform.

Signed-off-by: Amit Machhiwal <amachhiw@...ux.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 19f4d298dd17..7667563fb9ff 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -6541,10 +6541,6 @@ static struct kvmppc_ops kvm_ops_hv = {
 	.fast_vcpu_kick = kvmppc_fast_vcpu_kick_hv,
 	.arch_vm_ioctl  = kvm_arch_vm_ioctl_hv,
 	.hcall_implemented = kvmppc_hcall_impl_hv,
-#ifdef CONFIG_KVM_XICS
-	.irq_bypass_add_producer = kvmppc_irq_bypass_add_producer_hv,
-	.irq_bypass_del_producer = kvmppc_irq_bypass_del_producer_hv,
-#endif
 	.configure_mmu = kvmhv_configure_mmu,
 	.get_rmmu_info = kvmhv_get_rmmu_info,
 	.set_smt_mode = kvmhv_set_smt_mode,
@@ -6662,6 +6658,22 @@ static int kvmppc_book3s_init_hv(void)
 		return r;
 	}

+#if defined(CONFIG_KVM_XICS)
+	/*
+	 * IRQ bypass is supported only for interrupts whose EOI operations are
+	 * handled via OPAL calls. Therefore, register IRQ bypass handlers
+	 * exclusively for PowerNV KVM when booted with 'xive=off', indicating
+	 * the use of the emulated XICS interrupt controller.
+	 */
+	if (!kvmhv_on_pseries()) {
+		pr_info("KVM-HV: Enabling IRQ bypass\n");
+		kvm_ops_hv.irq_bypass_add_producer =
+			kvmppc_irq_bypass_add_producer_hv;
+		kvm_ops_hv.irq_bypass_del_producer =
+			kvmppc_irq_bypass_del_producer_hv;
+	}
+#endif
+
 	kvm_ops_hv.owner = THIS_MODULE;
 	kvmppc_hv_ops = &kvm_ops_hv;

base-commit: 6e3597f12dce7d5041e604fec3602493e38c330a
-- 
2.49.0