Subject: [PATCH v2 18/28] ARM: KVM: Add HYP mode entry code

From: [email-masked] (Christoffer Dall)
Date: Tue, 9 Feb 2016 18:00:42 +0100

On Thu, Feb 04, 2016 at 11:00:35AM +0000, Marc Zyngier wrote:
> This part is almost entierely borrowed from the existing code, just
> slightly simplifying the HYP function call (as we now save SPSR_hyp
> in the world switch).
> 
> Signed-off-by: Marc Zyngier <[email-masked]>
> ---
>  arch/arm/kvm/hyp/Makefile    |   1 +
>  arch/arm/kvm/hyp/hyp-entry.S | 157 +++++++++++++++++++++++++++++++++++++++++++
>  arch/arm/kvm/hyp/hyp.h       |   2 +
>  3 files changed, 160 insertions(+)
>  create mode 100644 arch/arm/kvm/hyp/hyp-entry.S
> 
> diff --git a/arch/arm/kvm/hyp/Makefile b/arch/arm/kvm/hyp/Makefile
> index cfab402..a7d3a7e 100644
> --- a/arch/arm/kvm/hyp/Makefile
> +++ b/arch/arm/kvm/hyp/Makefile
> @@ -9,4 +9,5 @@ obj-$(CONFIG_KVM_ARM_HOST) += vgic-v2-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += vfp.o
>  obj-$(CONFIG_KVM_ARM_HOST) += banked-sr.o
>  obj-$(CONFIG_KVM_ARM_HOST) += entry.o
> +obj-$(CONFIG_KVM_ARM_HOST) += hyp-entry.o
>  obj-$(CONFIG_KVM_ARM_HOST) += switch.o
> diff --git a/arch/arm/kvm/hyp/hyp-entry.S b/arch/arm/kvm/hyp/hyp-entry.S
> new file mode 100644
> index 0000000..44bc11f
> --- /dev/null
> +++ b/arch/arm/kvm/hyp/hyp-entry.S
> @@ -0,0 +1,157 @@
> +/*
> + * Copyright (C) 2012 - Virtual Open Systems and Columbia University
> + * Author: Christoffer Dall <[email-masked]>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License, version 2, as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
> + */
> +
> +#include <linux/linkage.h>
> +#include <asm/kvm_arm.h>
> +#include <asm/kvm_asm.h>
> +
> +	.arch_extension     virt
> +
> +	.text
> +	.pushsection	.hyp.text, "ax"
> +
> +.macro load_vcpu	reg
> +	mrc	p15, 4, \reg, c13, c0, 2	@ HTPIDR
> +.endm
> +
> +/********************************************************************
> + * Hypervisor exception vector and handlers
> + *
> + *
> + * The KVM/ARM Hypervisor ABI is defined as follows:
> + *
> + * Entry to Hyp mode from the host kernel will happen _only_ when an HVC
> + * instruction is issued since all traps are disabled when running the host
> + * kernel as per the Hyp-mode initialization at boot time.
> + *
> + * HVC instructions cause a trap to the vector page + offset 0x14 (see hyp_hvc
> + * below) when the HVC instruction is called from SVC mode (i.e. a guest or the
> + * host kernel) and they cause a trap to the vector page + offset 0x8 when HVC
> + * instructions are called from within Hyp-mode.
> + *
> + * Hyp-ABI: Calling HYP-mode functions from host (in SVC mode):
> + *    Switching to Hyp mode is done through a simple HVC #0 instruction. The
> + *    exception vector code will check that the HVC comes from VMID==0.
> + *    - r0 contains a pointer to a HYP function
> + *    - r1, r2, and r3 contain arguments to the above function.
> + *    - The HYP function will be called with its arguments in r0, r1 and r2.
> + *    On HYP function return, we return directly to SVC.
> + *
> + * Note that the above is used to execute code in Hyp-mode from a host-kernel
> + * point of view, and is a different concept from performing a world-switch and
> + * executing guest code SVC mode (with a VMID != 0).
> + */
> +
> +	.align 5
> +__hyp_vector:
> +	.global	__hyp_vector
> +__kvm_hyp_vector:
> +	.weak __kvm_hyp_vector
> +
> +	@ Hyp-mode exception vector
> +	W(b)	hyp_reset
> +	W(b)	hyp_undef
> +	W(b)	hyp_svc
> +	W(b)	hyp_pabt
> +	W(b)	hyp_dabt
> +	W(b)	hyp_hvc
> +	W(b)	hyp_irq
> +	W(b)	hyp_fiq
> +
> +.macro invalid_vector label, cause
> +	.align
> +\label:	b	.
> +.endm
> +
> +	invalid_vector	hyp_reset
> +	invalid_vector	hyp_undef
> +	invalid_vector	hyp_svc
> +	invalid_vector	hyp_pabt
> +	invalid_vector	hyp_dabt
> +	invalid_vector	hyp_fiq
> +
> +hyp_hvc:
> +	/*
> +	 * Getting here is either because of a trap from a guest,
> +	 * or from executing HVC from the host kernel, which means
> +	 * "do something in Hyp mode".
> +	 */
> +	push	{r0, r1, r2}
> +
> +	@ Check syndrome register
> +	mrc	p15, 4, r1, c5, c2, 0	@ HSR
> +	lsr	r0, r1, #HSR_EC_SHIFT
> +	cmp	r0, #HSR_EC_HVC
> +	bne	guest_trap		@ Not HVC instr.
> +
> +	/*
> +	 * Let's check if the HVC came from VMID 0 and allow simple
> +	 * switch to Hyp mode
> +	 */
> +	mrrc    p15, 6, r0, r2, c2
> +	lsr     r2, r2, #16
> +	and     r2, r2, #0xff
> +	cmp     r2, #0
> +	bne	guest_trap		@ Guest called HVC
> +
> +	/*
> +	 * Getting here means host called HVC, we shift parameters and branch
> +	 * to Hyp function.
> +	 */
> +	pop	{r0, r1, r2}
> +
> +	/* Check for __hyp_get_vectors */
> +	cmp	r0, #-1
> +	mrceq	p15, 4, r0, c12, c0, 0	@ get HVBAR
> +	beq	1f
> +
> +	push	{lr}
> +
> +	mov	lr, r0
> +	mov	r0, r1
> +	mov	r1, r2
> +	mov	r2, r3
> +
> +THUMB(	orr	lr, #1)
> +	blx	lr			@ Call the HYP function
> +
> +	pop	{lr}
> +1:	eret
> +
> +guest_trap:
> +	load_vcpu r0			@ Load VCPU pointer to r0
> +
> +	@ Check if we need the fault information

nit: this is not about faults at this point, so this comment should
either go or be reworded to "let's check if we trapped on guest VFP
access"

and I think the lsr can be moved into the ifdef as well.

> +	lsr	r1, r1, #HSR_EC_SHIFT
> +#ifdef CONFIG_VFPv3
> +	cmp	r1, #HSR_EC_CP_0_13
> +	beq	__vfp_guest_restore
> +#endif
> +
> +	mov	r1, #ARM_EXCEPTION_HVC
> +	b	__guest_exit
> +
> +hyp_irq:
> +	push	{r0, r1, r2}
> +	mov	r1, #ARM_EXCEPTION_IRQ
> +	load_vcpu r0			@ Load VCPU pointer to r0
> +	b	__guest_exit
> +
> +	.ltorg
> +
> +	.popsection
> diff --git a/arch/arm/kvm/hyp/hyp.h b/arch/arm/kvm/hyp/hyp.h
> index 7ddca54..8bbd2a7 100644
> --- a/arch/arm/kvm/hyp/hyp.h
> +++ b/arch/arm/kvm/hyp/hyp.h
> @@ -123,4 +123,6 @@ void __hyp_text __banked_restore_state(struct kvm_cpu_context *ctxt);
>  
>  int asmlinkage __guest_enter(struct kvm_vcpu *vcpu,
>  			     struct kvm_cpu_context *host);
> +int asmlinkage __hyp_do_panic(const char *, int, u32);
> +
>  #endif /* __ARM_KVM_HYP_H__ */
> -- 
> 2.1.4
> 
Otherwise looke good.

Thanks,
-Christoffer