linux-kernel - Re: [PATCH] KVM: x86: don't notify userspace IOAPIC on edge EOI

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Date:	Thu, 8 Oct 2015 20:34:54 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Steve Rutherford <srutherford@...gle.com>
Subject: Re: [PATCH] KVM: x86: don't notify userspace IOAPIC on edge EOI

2015-10-08 20:30+0200, Radim Krčmář:
> On real hardware, edge-triggered interrupts don't set a bit in TMR,
> which means that IOAPIC isn't notified on EOI.  Do the same here.
> 
> Staying in guest/kernel mode after edge EOI is what we want for most
> devices.  If some bugs could be nicely worked around with edge EOI
> notifications, we should invest in a better interface.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  Completely untested.
>  
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> @@ -389,13 +389,15 @@ void kvm_scan_ioapic_routes(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
>  	for (i = 0; i < nr_ioapic_pins; ++i) {
>  		hlist_for_each_entry(entry, &table->map[i], link) {
>  			u32 dest_id, dest_mode;
> +			bool level;
>  
>  			if (entry->type != KVM_IRQ_ROUTING_MSI)
>  				continue;
>  			dest_id = (entry->msi.address_lo >> 12) & 0xff;
>  			dest_mode = (entry->msi.address_lo >> 2) & 0x1;
> -			if (kvm_apic_match_dest(vcpu, NULL, 0, dest_id,
> -						dest_mode)) {
> +			level = entry->msi.data & MSI_DATA_TRIGGER_LEVEL;
> +			if (level && kvm_apic_match_dest(vcpu, NULL, 0,

Describing that result is an overkill -- I'll send v2 if the idea is
accepted.
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