linux-kernel - Re: [PATCH v5 19/23] KVM: arm64: GICv4.1: Allow SGIs to switch between HW and SW interrupts

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Message-ID: <877ba4711c6b9456314ea580b9c4718c@kernel.org>
Date:   Thu, 19 Mar 2020 19:52:41 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jason Cooper <jason@...edaemon.net>,
        Robert Richter <rrichter@...vell.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Zenghui Yu <yuzenghui@...wei.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH v5 19/23] KVM: arm64: GICv4.1: Allow SGIs to switch
 between HW and SW interrupts

Hi Eric,

On 2020-03-19 16:16, Auger Eric wrote:
> Hi Marc,
> 
> On 3/4/20 9:33 PM, Marc Zyngier wrote:
>> In order to let a guest buy in the new, active-less SGIs, we
>> need to be able to switch between the two modes.
>> 
>> Handle this by stopping all guest activity, transfer the state
>> from one mode to the other, and resume the guest. Nothing calls
>> this code so far, but a later patch will plug it into the MMIO
>> emulation.
>> 
>> Signed-off-by: Marc Zyngier <maz@...nel.org>
>> ---
>>  include/kvm/arm_vgic.h      |  3 ++
>>  virt/kvm/arm/vgic/vgic-v4.c | 94 
>> +++++++++++++++++++++++++++++++++++++
>>  virt/kvm/arm/vgic/vgic.h    |  1 +
>>  3 files changed, 98 insertions(+)
>> 
>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>> index 63457908c9c4..69f4164d6477 100644
>> --- a/include/kvm/arm_vgic.h
>> +++ b/include/kvm/arm_vgic.h
>> @@ -231,6 +231,9 @@ struct vgic_dist {
>>  	/* distributor enabled */
>>  	bool			enabled;
>> 
>> +	/* Wants SGIs without active state */
>> +	bool			nassgireq;
>> +
>>  	struct vgic_irq		*spis;
>> 
>>  	struct vgic_io_device	dist_iodev;
>> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
>> index c2fcde104ea2..a65dc1c85363 100644
>> --- a/virt/kvm/arm/vgic/vgic-v4.c
>> +++ b/virt/kvm/arm/vgic/vgic-v4.c
>> @@ -97,6 +97,100 @@ static irqreturn_t vgic_v4_doorbell_handler(int 
>> irq, void *info)
>>  	return IRQ_HANDLED;
>>  }
>> 
>> +static void vgic_v4_sync_sgi_config(struct its_vpe *vpe, struct 
>> vgic_irq *irq)
>> +{
>> +	vpe->sgi_config[irq->intid].enabled	= irq->enabled;
>> +	vpe->sgi_config[irq->intid].group 	= irq->group;
>> +	vpe->sgi_config[irq->intid].priority	= irq->priority;
>> +}
>> +
>> +static void vgic_v4_enable_vsgis(struct kvm_vcpu *vcpu)
>> +{
>> +	struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
>> +	int i;
>> +
>> +	/*
>> +	 * With GICv4.1, every virtual SGI can be directly injected. So
>> +	 * let's pretend that they are HW interrupts, tied to a host
>> +	 * IRQ. The SGI code will do its magic.
>> +	 */
>> +	for (i = 0; i < VGIC_NR_SGIS; i++) {
>> +		struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, i);
>> +		struct irq_desc *desc;
>> +		int ret;
> Is is safe without holding the irq->irq_lock?

The assumption here is that we're coming vgic_v4_configure_vsgis(), 
which starts
by stopping the whole guest. My guess is that it should be safe enough, 
but
maybe you are thinking of something else?

Thanks,

          M.
-- 
Jazz is not dead. It just smells funny...