linux-kernel - Re: [PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST

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Message-ID: <87eem3ozxd.fsf@nanos.tec.linutronix.de>
Date:   Tue, 13 Oct 2020 00:13:50 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw2@...radead.org>, x86@...nel.org,
        Marc Zyngier <maz@...nel.org>
Cc:     kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST_ID

On Mon, Oct 12 2020 at 21:20, David Woodhouse wrote:
> On Mon, 2020-10-12 at 20:38 +0200, Thomas Gleixner wrote:
>> Nasty, but way better than what we have now. 
>
> Want me to send that out in email or is the git tree enough for now?
>
> I've cleaned it up a little and fixed a bug in the I/OAPIC error path.

Mail would be nice once you are confident with the pile.

> Still not entirely convinced about the apic->apic_id_valid(32768) thing
> but it should work well enough, and doesn't require exporting any extra
> state from apic.c that way.

Yeah, that part is odd.

I really dislike the way how irq_find_matching_fwspec() works. The 'rc'
value is actually boolean despite being type 'int' and if 'rc' is not 0
then it returns the domain even if 'rc' is an error code.

But that does not allow to return error codes from a domain match() /
select() callback which is what we really want to express that there is
something fishy.

Something like the below perhaps? Needs more thought obviously.

Marc, any opinion ?

Thanks,

        tglx

8<-------------

arch/x86/kernel/apic/vector.c |   18 ++++++++++++++++++
 include/linux/irqdomain.h     |    1 +
 kernel/irq/irqdomain.c        |    2 +-
 3 files changed, 20 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -593,6 +593,24 @@ static int x86_vector_alloc_irqs(struct
 	return err;
 }
 
+struct irq_domain *x86_select_parent_domain(struct irq_fwspec *fwspec)
+{
+	struct irq_domain *dom;
+
+	/*
+	 * If Interrupt Remapping is enabled then the match function
+	 * returns either the remapping domain or an error code if the
+	 * device is not registered with the remapping unit.
+	 *
+	 * If remapping is not enabled, then the function returns NULL.
+	 */
+	dom = irq_find_matching_fwspec(fwspec, DOMAIN_BUS_IR);
+	if (dom)
+		return IS_ERR(dom) ? NULL : dom;
+
+	return x86_vector_domain;
+}
+
 #ifdef CONFIG_GENERIC_IRQ_DEBUGFS
 static void x86_vector_debug_show(struct seq_file *m, struct irq_domain *d,
 				  struct irq_data *irqd, int ind)
--- a/include/linux/irqdomain.h
+++ b/include/linux/irqdomain.h
@@ -85,6 +85,7 @@ enum irq_domain_bus_token {
 	DOMAIN_BUS_TI_SCI_INTA_MSI,
 	DOMAIN_BUS_WAKEUP,
 	DOMAIN_BUS_VMD_MSI,
+	DOMAIN_BUS_IR,
 };
 
 /**
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -395,7 +395,7 @@ struct irq_domain *irq_find_matching_fws
 			       (h->bus_token == bus_token)));
 
 		if (rc) {
-			found = h;
+			found = rc < 0 ? ERR_PTR(rc) : h;
 			break;
 		}
 	}