Re: [PATCH v3 05/19] KVM: arm64: ITS: Implement vgic_its_has_attr_regs and attr_regs_access

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Hi Eric,

On 06/03/17 11:34, Eric Auger wrote:
> This patch implements vgic_its_has_attr_regs and vgic_its_attr_regs_access
> upon the MMIO framework. VGIC ITS KVM device KVM_DEV_ARM_VGIC_GRP_ITS_REGS
> group becomes functional.
> 
> At least GITS_CREADR requires to differentiate a guest write action from a
> user access. As such let's introduce a new uaccess_its_write
> vgic_register_region callback.
> 
> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> ---
>  virt/kvm/arm/vgic/vgic-its.c  | 74 ++++++++++++++++++++++++++++++++++++-------
>  virt/kvm/arm/vgic/vgic-mmio.h |  9 ++++--
>  2 files changed, 69 insertions(+), 14 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 43bb17e..e9c8f9f 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -1287,13 +1287,14 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
>  	*regptr = reg;
>  }
>  
> -#define REGISTER_ITS_DESC(off, rd, wr, length, acc)		\
> +#define REGISTER_ITS_DESC(off, rd, wr, uwr, length, acc)		\
>  {								\
>  	.reg_offset = off,					\
>  	.len = length,						\
>  	.access_flags = acc,					\
>  	.its_read = rd,						\
>  	.its_write = wr,					\
> +	.uaccess_its_write = uwr,					\

I was wondering if it would create less churn to keep this definition
here (with .uaccess_its_write automatically becoming NULL), and then
either open-code the one special case below or provide a second wrapper
macro. But I guess either way is not really nice, so we could go with
this approach here as well.

>  }
>  
>  static void its_mmio_write_wi(struct kvm *kvm, struct vgic_its *its,
> @@ -1304,28 +1305,28 @@ static void its_mmio_write_wi(struct kvm *kvm, struct vgic_its *its,
>  
>  static struct vgic_register_region its_registers[] = {
>  	REGISTER_ITS_DESC(GITS_CTLR,
> -		vgic_mmio_read_its_ctlr, vgic_mmio_write_its_ctlr, 4,
> +		vgic_mmio_read_its_ctlr, vgic_mmio_write_its_ctlr, NULL, 4,
>  		VGIC_ACCESS_32bit),
>  	REGISTER_ITS_DESC(GITS_IIDR,
> -		vgic_mmio_read_its_iidr, its_mmio_write_wi, 4,
> +		vgic_mmio_read_its_iidr, its_mmio_write_wi, NULL, 4,
>  		VGIC_ACCESS_32bit),
>  	REGISTER_ITS_DESC(GITS_TYPER,
> -		vgic_mmio_read_its_typer, its_mmio_write_wi, 8,
> +		vgic_mmio_read_its_typer, its_mmio_write_wi, NULL, 8,
>  		VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
>  	REGISTER_ITS_DESC(GITS_CBASER,
> -		vgic_mmio_read_its_cbaser, vgic_mmio_write_its_cbaser, 8,
> +		vgic_mmio_read_its_cbaser, vgic_mmio_write_its_cbaser, NULL, 8,
>  		VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
>  	REGISTER_ITS_DESC(GITS_CWRITER,
> -		vgic_mmio_read_its_cwriter, vgic_mmio_write_its_cwriter, 8,
> -		VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
> +		vgic_mmio_read_its_cwriter, vgic_mmio_write_its_cwriter, NULL,
> +		8, VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
>  	REGISTER_ITS_DESC(GITS_CREADR,
> -		vgic_mmio_read_its_creadr, its_mmio_write_wi, 8,
> +		vgic_mmio_read_its_creadr, its_mmio_write_wi, NULL, 8,
>  		VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
>  	REGISTER_ITS_DESC(GITS_BASER,
> -		vgic_mmio_read_its_baser, vgic_mmio_write_its_baser, 0x40,
> +		vgic_mmio_read_its_baser, vgic_mmio_write_its_baser, NULL, 0x40,
>  		VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
>  	REGISTER_ITS_DESC(GITS_IDREGS_BASE,
> -		vgic_mmio_read_its_idregs, its_mmio_write_wi, 0x30,
> +		vgic_mmio_read_its_idregs, its_mmio_write_wi, NULL, 0x30,
>  		VGIC_ACCESS_32bit),
>  };
>  
> @@ -1448,14 +1449,63 @@ static void vgic_its_destroy(struct kvm_device *kvm_dev)
>  int vgic_its_has_attr_regs(struct kvm_device *dev,
>  			   struct kvm_device_attr *attr)
>  {
> -	return -ENXIO;
> +	const struct vgic_register_region *region;
> +	struct vgic_io_device iodev = {
> +		.regions = its_registers,
> +		.nr_regions = ARRAY_SIZE(its_registers),
> +	};
> +	gpa_t offset;
> +
> +	offset = attr->attr;

Those two can be on one line.
But actually why not just put attr->attr below and save that variable at
all?

> +
> +	region = vgic_find_mmio_region(iodev.regions,
> +				       iodev.nr_regions,
> +				       offset);
> +	if (!region)
> +		return -ENXIO;

Nit: empty line here?

> +	return 0;
>  }
>  
>  int vgic_its_attr_regs_access(struct kvm_device *dev,
>  			      struct kvm_device_attr *attr,
>  			      u64 *reg, bool is_write)
>  {
> -	return -ENXIO;
> +	const struct vgic_register_region *region;
> +	struct vgic_io_device iodev = {
> +		.regions = its_registers,
> +		.nr_regions = ARRAY_SIZE(its_registers),
> +	};
> +	struct vgic_its *its = dev->private;
> +	gpa_t addr, offset;
> +	unsigned int len;
> +
> +	if (IS_VGIC_ADDR_UNDEF(its->vgic_its_base))
> +		return -ENXIO;
> +
> +	offset = attr->attr;
> +	if (offset & 0x7)
> +		return -EINVAL;

Isn't this still breaking IIDR reads (a 32-bit register at offset 0x4)?

> +
> +	addr = its->vgic_its_base + offset;
> +
> +	region = vgic_find_mmio_region(iodev.regions,
> +				       iodev.nr_regions,
> +				       offset);
> +	if (!region)
> +		return -ENXIO;
> +
> +	len = region->access_flags & VGIC_ACCESS_64bit ? 8 : 4;

Can you add a comment that states that we only support full register
accesses via this interface (deviating from the spec which allows split
accesses to 64-bit registers)? I think that's mentioned somewhere else
(Documentation/...), but it avoids confusion for the casual reader here.

Also I am wondering if that way of using the pointer here for both 32-
and 64-bit registers breaks on big endian? Or is it specified somewhere
that this interface uses LE only?

The rest looks fine, thanks!

Cheers,
Andre.

> +	if (is_write) {
> +		if (region->uaccess_its_write)
> +			region->uaccess_its_write(dev->kvm, its, addr,
> +						  len, *reg);
> +		else
> +			region->its_write(dev->kvm, its, addr, len, *reg);
> +	} else {
> +		*reg = region->its_read(dev->kvm, its, addr, len);
> +	}
> +	return 0;
>  }
>  
>  static int vgic_its_has_attr(struct kvm_device *dev,
> diff --git a/virt/kvm/arm/vgic/vgic-mmio.h b/virt/kvm/arm/vgic/vgic-mmio.h
> index 055ad42..ad8a585 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio.h
> +++ b/virt/kvm/arm/vgic/vgic-mmio.h
> @@ -36,8 +36,13 @@ struct vgic_register_region {
>  	};
>  	unsigned long (*uaccess_read)(struct kvm_vcpu *vcpu, gpa_t addr,
>  				      unsigned int len);
> -	void (*uaccess_write)(struct kvm_vcpu *vcpu, gpa_t addr,
> -			      unsigned int len, unsigned long val);
> +	union {
> +		void (*uaccess_write)(struct kvm_vcpu *vcpu, gpa_t addr,
> +				      unsigned int len, unsigned long val);
> +		void (*uaccess_its_write)(struct kvm *kvm, struct vgic_its *its,
> +					  gpa_t addr, unsigned int len,
> +					  unsigned long val);
> +	};
>  };
>  
>  extern struct kvm_io_device_ops kvm_io_gic_ops;
> 



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