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

From: [email-masked] (Christoffer Dall)
Date: Wed, 10 Feb 2016 18:23:21 +0100

On Wed, Feb 10, 2016 at 04:02:14PM +0000, Marc Zyngier wrote:
> On 09/02/16 17:00, Christoffer Dall wrote:
> > 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.
> 
> Yes, both good points.
> 
fixing that, you can also have my

Reviewed-by: Christoffer Dall <[email-masked]>

if I didn't give it already.

-Christoffer