Subject: [PATCH v4 06/12] KVM: arm64: implement basic ITS register handlers

From: [email-masked] (Christoffer Dall)
Date: Sun, 3 Apr 2016 12:08:21 +0200

On Sat, Mar 26, 2016 at 02:14:04AM +0000, Andre Przywara wrote:
> Add emulation for some basic MMIO registers used in the ITS emulation.
> This includes:
> - GITS_{CTLR,TYPER,IIDR}
> - ID registers
> - GITS_{CBASER,CREADR,CWRITER}
>   those implement the ITS command buffer handling
> 
> Most of the handlers are pretty straight forward, but CWRITER goes
> some extra miles to allow fine grained locking. The idea here
> is to let only the first instance iterate through the command ring
> buffer, CWRITER accesses on other VCPUs meanwhile will be picked up
> by that first instance and handled as well. The ITS lock is thus only
> hold for very small periods of time and is dropped before the actual

s/hold/held/

> command handler is called.
> 
> Signed-off-by: Andre Przywara <[email-masked]>
> ---
>  include/kvm/vgic/vgic.h            |   3 +
>  include/linux/irqchip/arm-gic-v3.h |   8 ++
>  virt/kvm/arm/vgic/its-emul.c       | 272 ++++++++++++++++++++++++++++++++++++-
>  virt/kvm/arm/vgic/vgic.h           |   6 +
>  virt/kvm/arm/vgic/vgic_init.c      |   2 +
>  5 files changed, 284 insertions(+), 7 deletions(-)
> 
> diff --git a/include/kvm/vgic/vgic.h b/include/kvm/vgic/vgic.h
> index c79bed5..bafea11 100644
> --- a/include/kvm/vgic/vgic.h
> +++ b/include/kvm/vgic/vgic.h
> @@ -115,6 +115,9 @@ struct vgic_io_device {
>  struct vgic_its {
>  	bool			enabled;
>  	spinlock_t		lock;

exactly what does this lock protect?

> +	u64			cbaser;
> +	int			creadr;
> +	int			cwriter;
>  };
>  
>  struct vgic_dist {
> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
> index a813c3e..7011b98 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -179,15 +179,23 @@
>  #define GITS_BASER			0x0100
>  #define GITS_IDREGS_BASE		0xffd0
>  #define GITS_PIDR2			GICR_PIDR2
> +#define GITS_PIDR4			0xffd0
> +#define GITS_CIDR0			0xfff0
> +#define GITS_CIDR1			0xfff4
> +#define GITS_CIDR2			0xfff8
> +#define GITS_CIDR3			0xfffc
>  
>  #define GITS_TRANSLATER			0x10040
>  
>  #define GITS_CTLR_ENABLE		(1U << 0)
>  #define GITS_CTLR_QUIESCENT		(1U << 31)
>  
> +#define GITS_TYPER_PLPIS		(1UL << 0)
> +#define GITS_TYPER_IDBITS_SHIFT		8
>  #define GITS_TYPER_DEVBITS_SHIFT	13
>  #define GITS_TYPER_DEVBITS(r)		((((r) >> GITS_TYPER_DEVBITS_SHIFT) & 0x1f) + 1)
>  #define GITS_TYPER_PTA			(1UL << 19)
> +#define GITS_TYPER_HWCOLLCNT_SHIFT	24
>  
>  #define GITS_CBASER_VALID		(1UL << 63)
>  #define GITS_CBASER_nCnB		(0UL << 59)
> diff --git a/virt/kvm/arm/vgic/its-emul.c b/virt/kvm/arm/vgic/its-emul.c
> index 49dd5e4..de8d360 100644
> --- a/virt/kvm/arm/vgic/its-emul.c
> +++ b/virt/kvm/arm/vgic/its-emul.c
> @@ -31,23 +31,263 @@
>  #include "vgic.h"
>  #include "vgic_mmio.h"
>  
> +#define BASER_BASE_ADDRESS(x) ((x) & 0xfffffffff000ULL)
> +
> +static int vgic_mmio_read_its_ctlr(struct kvm_vcpu *vcpu,
> +				   struct kvm_io_device *this,
> +				   gpa_t addr, int len, void *val)
> +{
> +	struct vgic_its *its = &vcpu->kvm->arch.vgic.its;
> +	u32 reg;
> +
> +	reg = GITS_CTLR_QUIESCENT;
> +	if (its->enabled)
> +		reg |= GITS_CTLR_ENABLE;
> +
> +	write_mask32(reg, addr & 3, len, val);
> +
> +	return 0;
> +}
> +
> +static int vgic_mmio_write_its_ctlr(struct kvm_vcpu *vcpu,
> +				    struct kvm_io_device *this,
> +				    gpa_t addr, int len, const void *val)
> +{
> +	struct vgic_its *its = &vcpu->kvm->arch.vgic.its;
> +	struct vgic_io_device *iodev = container_of(this,
> +						    struct vgic_io_device, dev);
> +
> +        if (addr - iodev->base_addr == 0)
> +		its->enabled = !!(*(u8*)val & GITS_CTLR_ENABLE);
> +
> +	return 0;
> +}
> +
> +static int vgic_mmio_read_its_typer(struct kvm_vcpu *vcpu,
> +				    struct kvm_io_device *this,
> +				    gpa_t addr, int len, void *val)
> +{
> +	u64 reg = GITS_TYPER_PLPIS;
> +
> +	/*
> +	 * We use linear CPU numbers for redistributor addressing,
> +	 * so GITS_TYPER.PTA is 0.
> +	 * To avoid memory waste on the guest side, we keep the
> +	 * number of IDBits and DevBits low for the time being.
> +	 * This could later be made configurable by userland.
> +	 * Since we have all collections in linked list, we claim

s/linked list/linked lists/

is the point here not more specifically that we hold the data in kernel
data structures not visible by guest memory, rather than addressing
which specific data structure we use in the kernel?

> +	 * that we can hold all of the collection tables in our
> +	 * own memory and that the ITT entry size is 1 byte (the
> +	 * smallest possible one).
> +	 */
> +	reg |= 0xff << GITS_TYPER_HWCOLLCNT_SHIFT;
> +	reg |= 0x0f << GITS_TYPER_DEVBITS_SHIFT;
> +	reg |= 0x0f << GITS_TYPER_IDBITS_SHIFT;
> +
> +	write_mask64(reg, addr & 7, len, val);
> +
> +	return 0;
> +}
> +
> +static int vgic_mmio_read_its_iidr(struct kvm_vcpu *vcpu,
> +				   struct kvm_io_device *this,
> +				   gpa_t addr, int len, void *val)
> +{
> +	u32 reg = (PRODUCT_ID_KVM << 24) | (IMPLEMENTER_ARM << 0);
> +
> +	write_mask32(reg, addr & 3, len, val);
> +
> +	return 0;
> +}
> +
> +static int vgic_mmio_read_its_idregs(struct kvm_vcpu *vcpu,
> +				     struct kvm_io_device *this,
> +				     gpa_t addr, int len, void *val)
> +{
> +	struct vgic_io_device *iodev = container_of(this,
> +						    struct vgic_io_device, dev);
> +	u32 reg = 0;
> +	int idreg = (addr & ~3) - iodev->base_addr + GITS_IDREGS_BASE;
> +
> +	switch (idreg) {
> +	case GITS_PIDR2:
> +		reg = GIC_PIDR2_ARCH_GICv3;
> +		break;
> +	case GITS_PIDR4:
> +		/* This is a 64K software visible page */
> +		reg = 0x40;
> +		break;
> +	/* Those are the ID registers for (any) GIC. */
> +	case GITS_CIDR0:
> +		reg = 0x0d;
> +		break;
> +	case GITS_CIDR1:
> +		reg = 0xf0;
> +		break;
> +	case GITS_CIDR2:
> +		reg = 0x05;
> +		break;
> +	case GITS_CIDR3:
> +		reg = 0xb1;
> +		break;
> +	}
> +
> +	write_mask32(reg, addr & 3, len, val);
> +
> +	return 0;
> +}
> +
> +/*
> + * This function is called with both the ITS and the distributor lock dropped,
> + * so the actual command handlers must take the respective locks when needed.
> + */

I don't understand this comment.  Are these requirements for the locking
situation when entering this function or is explaining when this
function is called?

> +static int vits_handle_command(struct kvm_vcpu *vcpu, u64 *its_cmd)
> +{
> +	return -ENODEV;
> +}
> +
> +static int vgic_mmio_read_its_cbaser(struct kvm_vcpu *vcpu,
> +				    struct kvm_io_device *this,
> +				    gpa_t addr, int len, void *val)
> +{
> +	struct vgic_its *its = &vcpu->kvm->arch.vgic.its;
> +
> +	write_mask64(its->cbaser, addr & 7, len, val);
> +
> +	return 0;
> +}
> +
> +static int vgic_mmio_write_its_cbaser(struct kvm_vcpu *vcpu,
> +				      struct kvm_io_device *this,
> +				      gpa_t addr, int len, const void *val)
> +{
> +	struct vgic_its *its = &vcpu->kvm->arch.vgic.its;
> +
> +	if (its->enabled)
> +		return 0;
> +
> +	its->cbaser = mask64(its->cbaser, addr & 7, len, val);
> +	its->creadr = 0;
> +
> +	return 0;
> +}
> +
> +static int its_cmd_buffer_size(struct kvm *kvm)
> +{
> +	struct vgic_its *its = &kvm->arch.vgic.its;
> +
> +	return ((its->cbaser & 0xff) + 1) << 12;
> +}
> +
> +static gpa_t its_cmd_buffer_base(struct kvm *kvm)
> +{
> +	struct vgic_its *its = &kvm->arch.vgic.its;
> +
> +	return BASER_BASE_ADDRESS(its->cbaser);
> +}
> +
> +/*
> + * By writing to CWRITER the guest announces new commands to be processed.
> + * Since we cannot read from guest memory inside the ITS spinlock, we
> + * iterate over the command buffer (with the lock dropped) until the read
> + * pointer matches the write pointer. Other VCPUs writing this register in the
> + * meantime will just update the write pointer, leaving the command
> + * processing to the first instance of the function.
> + */
> +static int vgic_mmio_write_its_cwriter(struct kvm_vcpu *vcpu,
> +				       struct kvm_io_device *this,
> +				       gpa_t addr, int len, const void *val)
> +{
> +	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +	struct vgic_its *its = &dist->its;
> +	gpa_t cbaser = its_cmd_buffer_base(vcpu->kvm);
> +	u64 cmd_buf[4];
> +	u32 reg;
> +	bool finished;
> +
> +	reg = mask64(its->cwriter & 0xfffe0, addr & 7, len, val);
> +	reg &= 0xfffe0;
> +	if (reg > its_cmd_buffer_size(vcpu->kvm))
> +		return 0;
> +
> +	spin_lock(&its->lock);
> +
> +	/*
> +	 * If there is still another VCPU handling commands, let this
> +	 * one pick up the new CWRITER and process "our" new commands as well.
> +	 */
> +	finished = (its->cwriter != its->creadr);
> +	its->cwriter = reg;
> +
> +	spin_unlock(&its->lock);
> +
> +	while (!finished) {
> +		int ret = kvm_read_guest(vcpu->kvm, cbaser + its->creadr,
> +					 cmd_buf, 32);
> +		if (ret) {
> +			/*
> +			 * Gah, we are screwed. Reset CWRITER to that command

s/that/the/

> +			 * that we have finished processing and return.
> +			 */

what does this situation mean? That the guest programmed bogus values
into GITS_BASERn, or?  (Is that allowed?)

> +			spin_lock(&its->lock);
> +			its->cwriter = its->creadr;
> +			spin_unlock(&its->lock);
> +			break;
> +		}
> +		vits_handle_command(vcpu, cmd_buf);
> +
> +		spin_lock(&its->lock);
> +		its->creadr += 32;
> +		if (its->creadr == its_cmd_buffer_size(vcpu->kvm))
> +			its->creadr = 0;
> +		finished = (its->creadr == its->cwriter);
> +		spin_unlock(&its->lock);
> +	}
> +
> +	return 0;
> +}
> +
> +static int vgic_mmio_read_its_cwriter(struct kvm_vcpu *vcpu,
> +				      struct kvm_io_device *this,
> +				      gpa_t addr, int len, void *val)
> +{
> +	struct vgic_its *its = &vcpu->kvm->arch.vgic.its;
> +	u64 reg = its->cwriter & 0xfffe0;
> +
> +	write_mask64(reg, addr & 7, len, val);
> +
> +	return 0;
> +}
> +
> +static int vgic_mmio_read_its_creadr(struct kvm_vcpu *vcpu,
> +				     struct kvm_io_device *this,
> +				     gpa_t addr, int len, void *val)
> +{
> +	struct vgic_its *its = &vcpu->kvm->arch.vgic.its;
> +	u64 reg = its->creadr & 0xfffe0;
> +
> +	write_mask64(reg, addr & 7, len, val);
> +
> +	return 0;
> +}
> +
>  struct vgic_register_region its_registers[] = {
>  	REGISTER_DESC_WITH_LENGTH(GITS_CTLR,
> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 4),
> +		vgic_mmio_read_its_ctlr, vgic_mmio_write_its_ctlr, 4),
>  	REGISTER_DESC_WITH_LENGTH(GITS_IIDR,
> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 4),
> +		vgic_mmio_read_its_iidr, vgic_mmio_write_wi, 4),
>  	REGISTER_DESC_WITH_LENGTH(GITS_TYPER,
> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 4),
> +		vgic_mmio_read_its_typer, vgic_mmio_write_wi, 4),
>  	REGISTER_DESC_WITH_LENGTH(GITS_CBASER,
> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 8),
> +		vgic_mmio_read_its_cbaser, vgic_mmio_write_its_cbaser, 8),
>  	REGISTER_DESC_WITH_LENGTH(GITS_CWRITER,
> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 8),
> +		vgic_mmio_read_its_cwriter, vgic_mmio_write_its_cwriter, 8),
>  	REGISTER_DESC_WITH_LENGTH(GITS_CREADR,
> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 8),
> +		vgic_mmio_read_its_creadr, vgic_mmio_write_wi, 8),
>  	REGISTER_DESC_WITH_LENGTH(GITS_BASER,
>  		vgic_mmio_read_raz, vgic_mmio_write_wi, 0x40),
>  	REGISTER_DESC_WITH_LENGTH(GITS_IDREGS_BASE,
> -		vgic_mmio_read_raz, vgic_mmio_write_wi, 0x30),
> +		vgic_mmio_read_its_idregs, vgic_mmio_write_wi, 0x30),
>  };
>  
>  /* This is called on setting the LPI enable bit in the redistributor. */
> @@ -59,9 +299,14 @@ int vits_init(struct kvm *kvm)
>  {
>  	struct vgic_dist *dist = &kvm->arch.vgic;
>  	struct vgic_its *its = &dist->its;
> +	int nr_vcpus = atomic_read(&kvm->online_vcpus);
>  	struct vgic_io_device *regions;
>  	int ret, i;
>  
> +	dist->pendbaser = kcalloc(nr_vcpus, sizeof(u64), GFP_KERNEL);
> +	if (!dist->pendbaser)
> +		return -ENOMEM;
> +
>  	spin_lock_init(&its->lock);
>  
>  	regions = kmalloc_array(ARRAY_SIZE(its_registers),
> @@ -82,3 +327,16 @@ int vits_init(struct kvm *kvm)
>  
>  	return -ENXIO;
>  }
> +
> +void vits_destroy(struct kvm *kvm)
> +{
> +	struct vgic_dist *dist = &kvm->arch.vgic;
> +	struct vgic_its *its = &dist->its;
> +
> +	if (!vgic_has_its(kvm))
> +		return;
> +
> +	kfree(dist->pendbaser);
> +
> +	its->enabled = false;
> +}
> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
> index 4e7dcb8..08f97d1 100644
> --- a/virt/kvm/arm/vgic/vgic.h
> +++ b/virt/kvm/arm/vgic/vgic.h
> @@ -63,6 +63,7 @@ int vgic_register_redist_regions(struct kvm *kvm, gpa_t dist_base_address);
>  
>  int vits_init(struct kvm *kvm);
>  void vgic_enable_lpis(struct kvm_vcpu *vcpu);
> +void vits_destroy(struct kvm *kvm);
>  #else
>  static inline void vgic_v3_irq_change_affinity(struct kvm *kvm, u32 intid,
>  					       u64 mpidr)
> @@ -137,6 +138,11 @@ static inline void vgic_enable_lpis(struct kvm_vcpu *vcpu)
>  {
>  	return;
>  }
> +
> +static inline void vits_destroy(struct kvm *kvm)
> +{
> +	return;
> +}
>  #endif
>  
>  void vgic_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcr);
> diff --git a/virt/kvm/arm/vgic/vgic_init.c b/virt/kvm/arm/vgic/vgic_init.c
> index dcfb93d..e4459e3 100644
> --- a/virt/kvm/arm/vgic/vgic_init.c
> +++ b/virt/kvm/arm/vgic/vgic_init.c
> @@ -298,6 +298,8 @@ void kvm_vgic_destroy(struct kvm *kvm)
>  
>  	kvm_vgic_dist_destroy(kvm);
>  
> +	vits_destroy(kvm);
> +
>  	kvm_for_each_vcpu(i, vcpu, kvm)
>  		kvm_vgic_vcpu_destroy(vcpu);
>  }
> -- 
> 2.7.3
>