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

From: Paolo Bonzini <pbonzini@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>, linux-kernel@vger.kernel.org
Cc: kvm@vger.kernel.org, Steve Rutherford <srutherford@google.com>
Subject: Re: [PATCH] KVM: x86: don't notify userspace IOAPIC on edge EOI
Date: Fri, 9 Oct 2015 13:03:42 +0200	[thread overview]
Message-ID: <56179F0E.4050801@redhat.com> (raw)
In-Reply-To: <20151008183453.GD4508@potion.brq.redhat.com>

On 08/10/2015 20:34, Radim Krčmář wrote:
> 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@redhat.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.

It's okay and it matches the other lines before.  I'm applying this too,
but I would appreciate Steve's Tested-by before moving it to kvm/next.

Paolo