[PATCH v4 17/19] arm64: KVM: add SGI generation register emulation

[andre.przywara@arm.com (Andre Przywara)]

Hi,

On 23/11/14 15:08, Christoffer Dall wrote:
> On Fri, Nov 14, 2014 at 10:08:01AM +0000, Andre Przywara wrote:
>> While the generation of a (virtual) inter-processor interrupt (SGI)
>> on a GICv2 works by writing to a MMIO register, GICv3 uses the system
>> register ICC_SGI1R_EL1 to trigger them.
>> Trap that register on ARM64 hosts and handle it in a new handler
>> function in the GICv3 emulation code.
> 
> Did you reorder something or does my previous comment still apply that
> you're not enabling trapping yet, you're just adding the handler - those
> are two different things.

Yes, I can fix the wording.

> You sort of left my question about access_gic_sgi() not checking if the
> gicv3 is presetn hanging from the last thread, but I think I'm
> understanding properly now, that as long as you're not setting the
> ICC_SRE_EL2.Enable = 1, then we'll never get here, right?

Right, that is the idea. Just to make sure that I got this right from
the discussion the other day: We will not trap to EL2 as long as
ICC_SRE_EL2.Enable is 0 - which it should still be at this point, right?
(I am asking because I struggle to find this in the spec).

So actually your ICC_SRE_EL1 trap patch solved that problem ;-)

>>
>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>> ---
>> Changelog v3...v4:
>> - moved addition of vgic_v3_dispatch_sgi() from earlier patch into here
>> - move MPIDR comparison into extra function
>> - use new ICC_SGI1R_ field names
>> - improve readability of vgic_v3_dispatch_sgi()
>> - add and refine comments
>>
>>  arch/arm64/kvm/sys_regs.c   |   26 ++++++++++
>>  include/kvm/arm_vgic.h      |    1 +
>>  virt/kvm/arm/vgic-v3-emul.c |  113 +++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 140 insertions(+)
>>
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index fd3ffc3..e59369a 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -165,6 +165,27 @@ static bool access_sctlr(struct kvm_vcpu *vcpu,
>>  	return true;
>>  }
>>  
>> +/*
>> + * Trap handler for the GICv3 SGI generation system register.
>> + * Forward the request to the VGIC emulation.
>> + * The cp15_64 code makes sure this automatically works
>> + * for both AArch64 and AArch32 accesses.
>> + */
>> +static bool access_gic_sgi(struct kvm_vcpu *vcpu,
>> +			   const struct sys_reg_params *p,
>> +			   const struct sys_reg_desc *r)
>> +{
>> +	u64 val;
>> +
>> +	if (!p->is_write)
>> +		return read_from_write_only(vcpu, p);
>> +
>> +	val = *vcpu_reg(vcpu, p->Rt);
>> +	vgic_v3_dispatch_sgi(vcpu, val);
>> +
>> +	return true;
>> +}
>> +
>>  static bool trap_raz_wi(struct kvm_vcpu *vcpu,
>>  			const struct sys_reg_params *p,
>>  			const struct sys_reg_desc *r)
>> @@ -431,6 +452,9 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>>  	/* VBAR_EL1 */
>>  	{ Op0(0b11), Op1(0b000), CRn(0b1100), CRm(0b0000), Op2(0b000),
>>  	  NULL, reset_val, VBAR_EL1, 0 },
>> +	/* ICC_SGI1R_EL1 */
>> +	{ Op0(0b11), Op1(0b000), CRn(0b1100), CRm(0b1011), Op2(0b101),
>> +	  access_gic_sgi },
>>  	/* CONTEXTIDR_EL1 */
>>  	{ Op0(0b11), Op1(0b000), CRn(0b1101), CRm(0b0000), Op2(0b001),
>>  	  access_vm_reg, reset_val, CONTEXTIDR_EL1, 0 },
>> @@ -659,6 +683,8 @@ static const struct sys_reg_desc cp14_64_regs[] = {
>>   * register).
>>   */
>>  static const struct sys_reg_desc cp15_regs[] = {
>> +	{ Op1( 0), CRn( 0), CRm(12), Op2( 0), access_gic_sgi },
>> +
>>  	{ Op1( 0), CRn( 1), CRm( 0), Op2( 0), access_sctlr, NULL, c1_SCTLR },
>>  	{ Op1( 0), CRn( 2), CRm( 0), Op2( 0), access_vm_reg, NULL, c2_TTBR0 },
>>  	{ Op1( 0), CRn( 2), CRm( 0), Op2( 1), access_vm_reg, NULL, c2_TTBR1 },
>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>> index c1ef5a9..357a935 100644
>> --- a/include/kvm/arm_vgic.h
>> +++ b/include/kvm/arm_vgic.h
>> @@ -305,6 +305,7 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu);
>>  void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu);
>>  int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
>>  			bool level);
>> +void vgic_v3_dispatch_sgi(struct kvm_vcpu *vcpu, u64 reg);
>>  int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu);
>>  bool vgic_handle_mmio(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  		      struct kvm_exit_mmio *mmio);
>> diff --git a/virt/kvm/arm/vgic-v3-emul.c b/virt/kvm/arm/vgic-v3-emul.c
>> index 97b5801..58d7457 100644
>> --- a/virt/kvm/arm/vgic-v3-emul.c
>> +++ b/virt/kvm/arm/vgic-v3-emul.c
>> @@ -828,6 +828,119 @@ int vgic_v3_init_emulation(struct kvm *kvm)
>>  	return 0;
>>  }
>>  
>> +/*
>> + * Compare a given affinity (level 1-3 and a level 0 mask, from the SGI
>> + * generation register ICC_SGI1R_EL1) with a given VCPU.
>> + * If the VCPU's MPIDR matches, return the level0 affinity, otherwise
>> + * return -1.
>> + */
>> +static int match_mpidr(u64 sgi_aff, u16 sgi_cpu_mask, struct kvm_vcpu *vcpu)
>> +{
>> +	unsigned long affinity;
>> +	int level0;
>> +
>> +	/*
>> +	 * Split the current VCPU's MPIDR into affinity level 0 and the
>> +	 * rest as this is what we have to compare against.
>> +	 */
>> +	affinity = kvm_vcpu_get_mpidr_aff(vcpu);
>> +	level0 = MPIDR_AFFINITY_LEVEL(affinity, 0);
>> +	affinity &= ~MPIDR_LEVEL_MASK;
>> +
>> +	/* bail out if the upper three levels don't match */
>> +	if (sgi_aff != affinity)
>> +		return -1;
>> +
>> +	/* Is this VCPU's bit set in the mask ? */
>> +	if (!(sgi_cpu_mask & BIT(level0)))
>> +		return -1;
>> +
>> +	return level0;
>> +}
>> +
>> +#define SGI_AFFINITY_LEVEL(reg, level) \
>> +	((((reg) & ICC_SGI1R_AFFINITY_## level ##_MASK) \
>> +	>> ICC_SGI1R_AFFINITY_## level ##_SHIFT) << MPIDR_LEVEL_SHIFT(level))
>> +
>> +/**
>> + * vgic_v3_dispatch_sgi - handle SGI requests from VCPUs
>> + * @vcpu: The VCPU requesting a SGI
>> + * @reg: The value written into the ICC_SGI1R_EL1 register by that VCPU
>> + *
>> + * With GICv3 (and ARE=1) CPUs trigger SGIs by writing to an architectural
> 
> what's a non-architectural system register?

architectural vs. implementation defined.
Are you suggesting that I should drop "architectural" because it is a
tautology?

>> + * system register. This will trap in sys_regs.c and call this function.
>> + * This ICC_SGI1R_EL1 register contains the upper three affinity levels of the
>> + * target processors as well as a bitmask of 16 Aff0 CPUs.
>> + * If the interrupt routing mode bit is not set, we iterate over all VCPUs to
>> + * check for matching ones. If this bit is set, we signal all, but not the
>> + * calling VCPU.
>> + */
>> +void vgic_v3_dispatch_sgi(struct kvm_vcpu *vcpu, u64 reg)
>> +{
>> +	struct kvm *kvm = vcpu->kvm;
>> +	struct kvm_vcpu *c_vcpu;
>> +	struct vgic_dist *dist = &kvm->arch.vgic;
>> +	u16 target_cpus;
>> +	u64 mpidr;
>> +	int sgi, c, vcpu_id;
>> +	bool broadcast;
>> +	int updated = 0;
>> +
>> +	vcpu_id = vcpu->vcpu_id;
>> +
>> +	sgi = (reg & ICC_SGI1R_SGI_ID_MASK) >> ICC_SGI1R_SGI_ID_SHIFT;
>> +	broadcast = reg & BIT(ICC_SGI1R_IRQ_ROUTING_MODE_BIT);
>> +	target_cpus = (reg & ICC_SGI1R_TARGET_LIST_MASK) >> ICC_SGI1R_TARGET_LIST_SHIFT;
>> +	mpidr = SGI_AFFINITY_LEVEL(reg, 3);
>> +	mpidr |= SGI_AFFINITY_LEVEL(reg, 2);
>> +	mpidr |= SGI_AFFINITY_LEVEL(reg, 1);
>> +	mpidr &= ~MPIDR_LEVEL_MASK;
> 
> do you need this last mask?  It should be 0 already, right?

Indeed, I can drop this.

Thanks for looking at this!
Andre.

>> +
>> +	/*
>> +	 * We take the dist lock here, because we come from the sysregs
>> +	 * code path and not from the MMIO one (which already takes the lock).
>> +	 */
>> +	spin_lock(&dist->lock);
>> +
>> +	/*
>> +	 * We iterate over all VCPUs to find the MPIDRs matching the request.
>> +	 * If we have handled one CPU, we clear it's bit to detect early
>> +	 * if we are already finished. This avoids iterating through all
>> +	 * VCPUs when most of the times we just signal a single VCPU.
>> +	 */
>> +	kvm_for_each_vcpu(c, c_vcpu, kvm) {
>> +
>> +		/* Exit early if we have dealt with all requested CPUs */
>> +		if (!broadcast && target_cpus == 0)
>> +			break;
>> +
>> +		 /* Don't signal the calling VCPU */
>> +		if (broadcast && c == vcpu_id)
>> +			continue;
>> +
>> +		if (!broadcast) {
>> +			int level0;
>> +
>> +			level0 = match_mpidr(mpidr, target_cpus, c_vcpu);
>> +			if (level0 == -1)
>> +				continue;
>> +
>> +			/* remove this matching VCPU from the mask */
>> +			target_cpus &= ~BIT(level0);
>> +		}
>> +
>> +		/* Flag the SGI as pending */
>> +		vgic_dist_irq_set_pending(c_vcpu, sgi);
>> +		updated = 1;
>> +		kvm_debug("SGI%d from CPU%d to CPU%d\n", sgi, vcpu_id, c);
>> +	}
>> +	if (updated)
>> +		vgic_update_state(vcpu->kvm);
>> +	spin_unlock(&dist->lock);
>> +	if (updated)
>> +		vgic_kick_vcpus(vcpu->kvm);
>> +}
>> +
>>  static int vgic_v3_create(struct kvm_device *dev, u32 type)
>>  {
>>  	return kvm_vgic_create(dev->kvm, type);
>> -- 
>> 1.7.9.5
>>
> 
> Assuming you'll address the commit message stuff above:
> 
> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
>