[PATCH 00/20] arm/arm64: KVM: Rework the hyp-stub API

[PATCH 00/20] arm/arm64: KVM: Rework the hyp-stub API

[Marc Zyngier]

As noticed by RMK in this thread[1], the hyp-stub API on 32bit ARM
could do with some TLC (it cannot perform a soft-restart at HYP, and
has holes in the hyp-stub support in a number of places).

This series implements the following:
- Add HVC_[GS]ET_VECTORS and HVC_SOFT_RESTART to the 32bit code
- Add HVC_RESET_VECTORS to both arm and arm64, removing the need for
  __hyp_reset_vectors
- Implement add the stub entry points in the KVM init code, which
  didn't implement any so far
- Convert the HYP code to use the init code stubs directly
- Add some API documentation that covers the above

Patches 9 and 10 would be better squashed into 7 and 8, but I've kept
separate so that I can take the blame for everything I've broken.

This has been tested on arm and arm64, both as host and guest.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-December/473472.html

Marc Zyngier (18):
  arm64: hyp-stub: Implement HVC_RESET_VECTORS stub hypercall
  arm64: KVM: Implement HVC_RESET_VECTORS stub hypercall
  arm64: KVM: Implement HVC_GET_VECTORS in the init code
  arm64: KVM: Allow the main HYP code to use the init hyp stub
    implementation
  arm64: KVM: Convert __cpu_reset_hyp_mode to using __hyp_reset_vectors
  arm64: KVM: Implement HVC_SOFT_RESTART in the init code
  ARM: KVM: Convert KVM to use HVC_GET_VECTORS
  ARM: hyp-stub: Use r1 for the soft-restart address
  ARM: Expose the VA/IDMAP offset
  ARM: hyp-stub: Implement HVC_RESET_VECTORS stub hypercall
  ARM: KVM: Implement HVC_RESET_VECTORS stub hypercall
  ARM: KVM: Implement HVC_GET_VECTORS in the init code
  ARM: KVM: Allow the main HYP code to use the init hyp stub
    implementation
  ARM: KVM: Convert __cpu_reset_hyp_mode to using __hyp_reset_vectors
  ARM: KVM: Implement HVC_SOFT_RESTART in the init code
  arm/arm64: KVM: Simplify __cpu_reset_hyp_mode
  arm/arm64: KVM: Remove kvm_get_idmap_start
  arm/arm64: Add hyp-stub API documentation

Russell King (2):
  ARM: hyp-stub: improve ABI
  ARM: soft-reboot into same mode that we entered the kernel

 Documentation/virtual/kvm/arm/hyp-abi.txt | 48 +++++++++++++++++++++++++
 arch/arm/include/asm/kvm_asm.h            |  2 --
 arch/arm/include/asm/kvm_host.h           |  6 ++--
 arch/arm/include/asm/kvm_mmu.h            |  1 -
 arch/arm/include/asm/proc-fns.h           |  4 +--
 arch/arm/include/asm/virt.h               | 11 ++++++
 arch/arm/kernel/hyp-stub.S                | 44 ++++++++++++++++++++---
 arch/arm/kernel/reboot.c                  |  7 ++--
 arch/arm/kvm/arm.c                        |  3 +-
 arch/arm/kvm/hyp/hyp-entry.S              | 29 +++++++++++++---
 arch/arm/kvm/init.S                       | 58 ++++++++++++++++++++++++++-----
 arch/arm/kvm/mmu.c                        |  5 ---
 arch/arm/mm/mmu.c                         |  5 +++
 arch/arm/mm/proc-v7.S                     | 12 ++++---
 arch/arm64/include/asm/kvm_asm.h          |  1 -
 arch/arm64/include/asm/kvm_host.h         |  7 ++--
 arch/arm64/include/asm/kvm_mmu.h          |  1 -
 arch/arm64/include/asm/virt.h             |  8 +++++
 arch/arm64/kernel/hyp-stub.S              | 13 ++++++-
 arch/arm64/kvm/hyp-init.S                 | 50 ++++++++++++++++++++------
 arch/arm64/kvm/hyp/hyp-entry.S            | 39 ++++++++++-----------
 21 files changed, 278 insertions(+), 76 deletions(-)
 create mode 100644 Documentation/virtual/kvm/arm/hyp-abi.txt

-- 
2.11.0

[PATCH 01/20] arm64: hyp-stub: Implement HVC_RESET_VECTORS stub hypercall

[Marc Zyngier]

Let's define a new stub hypercall that resets the HYP configuration
to its default: hyp-stub vectors, and MMU disabled.

Of course, for the hyp-stub itself, this is a trivial no-op.
Hypervisors will have a bit more work to do.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm64/include/asm/virt.h |  8 ++++++++
 arch/arm64/kernel/hyp-stub.S  | 13 ++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 439f6b5d31f6..6d085a4d6cf1 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -39,6 +39,14 @@
  */
 #define HVC_SOFT_RESTART 2
 
+/*
+ * HVC_RESET_VECTORS - Restore the vectors to the original HYP stubs
+ */
+#define HVC_RESET_VECTORS 3
+
+/* Max number of HYP stub hypercalls */
+#define HVC_STUB_HCALL_NR 4
+
 #define BOOT_CPU_MODE_EL1	(0xe11)
 #define BOOT_CPU_MODE_EL2	(0xe12)
 
diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index d3b5f75e652e..a162182d5662 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -79,8 +79,11 @@ el1_sync:
 	mov	x1, x3
 	br	x4				// no return
 
+3:	cmp	x0, #HVC_RESET_VECTORS
+	beq	9f				// Nothing to reset!
+
 	/* Someone called kvm_call_hyp() against the hyp-stub... */
-3:	mov	x0, #ARM_EXCEPTION_HYP_GONE
+	mov	x0, #ARM_EXCEPTION_HYP_GONE
 
 9:	eret
 ENDPROC(el1_sync)
@@ -137,3 +140,11 @@ ENTRY(__hyp_set_vectors)
 	ldr	lr, [sp], #16
 	ret
 ENDPROC(__hyp_set_vectors)
+
+ENTRY(__hyp_reset_vectors)
+	str	lr, [sp, #-16]!
+	mov	x0, #HVC_RESET_VECTORS
+	hvc	#0
+	ldr	lr, [sp], #16
+	ret
+ENDPROC(__hyp_reset_vectors)
-- 
2.11.0

[PATCH 02/20] arm64: KVM: Implement HVC_RESET_VECTORS stub hypercall

[Marc Zyngier]

In order to restore HYP mode to its original condition, KVM currently
implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
defined API, it becomes necessary to implement HVC_RESET_VECTORS.

This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
code, which so far lacked any form of hypercall support.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm64/kvm/hyp-init.S | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
index 6b29d3d9e1f2..948f331c7f32 100644
--- a/arch/arm64/kvm/hyp-init.S
+++ b/arch/arm64/kvm/hyp-init.S
@@ -22,6 +22,7 @@
 #include <asm/kvm_mmu.h>
 #include <asm/pgtable-hwdef.h>
 #include <asm/sysreg.h>
+#include <asm/virt.h>
 
 	.text
 	.pushsection	.hyp.idmap.text, "ax"
@@ -58,6 +59,9 @@ __invalid:
 	 * x2: HYP vectors
 	 */
 __do_hyp_init:
+	/* Check for a stub HVC call */
+	cmp	x2, #HVC_STUB_HCALL_NR
+	b.lo	__kvm_handle_stub_hvc
 
 	msr	ttbr0_el2, x0
 
@@ -119,6 +123,9 @@ __do_hyp_init:
 	eret
 ENDPROC(__kvm_hyp_init)
 
+ENTRY(__kvm_handle_stub_hvc)
+	cmp	x0, #HVC_RESET_VECTORS
+	b.ne	1f
 	/*
 	 * Reset kvm back to the hyp stub.
 	 */
@@ -133,9 +140,14 @@ ENTRY(__kvm_hyp_reset)
 	/* Install stub vectors */
 	adr_l	x0, __hyp_stub_vectors
 	msr	vbar_el2, x0
+	b	exit
 
+1:	mov	x0, #-1
+
+exit:
 	eret
 ENDPROC(__kvm_hyp_reset)
+ENDPROC(__kvm_handle_stub_hvc)
 
 	.ltorg
 
-- 
2.11.0

[PATCH 02/20] arm64: KVM: Implement HVC_RESET_VECTORS stub hypercall

[James Morse]

Hi Marc,

On 17/02/17 15:44, Marc Zyngier wrote:
> In order to restore HYP mode to its original condition, KVM currently
> implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
> defined API, it becomes necessary to implement HVC_RESET_VECTORS.
> 
> This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
> code, which so far lacked any form of hypercall support.

> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index 6b29d3d9e1f2..948f331c7f32 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -58,6 +59,9 @@ __invalid:
>  	 * x2: HYP vectors
>  	 */
>  __do_hyp_init:
> +	/* Check for a stub HVC call */
> +	cmp	x2, #HVC_STUB_HCALL_NR

Nit: x2 -> x0?


> +	b.lo	__kvm_handle_stub_hvc
>  
>  	msr	ttbr0_el2, x0
>  
> @@ -119,6 +123,9 @@ __do_hyp_init:
>  	eret
>  ENDPROC(__kvm_hyp_init)
>  
> +ENTRY(__kvm_handle_stub_hvc)
> +	cmp	x0, #HVC_RESET_VECTORS
> +	b.ne	1f
>  	/*
>  	 * Reset kvm back to the hyp stub.
>  	 */

Thanks,

James

[PATCH 03/20] arm64: KVM: Implement HVC_GET_VECTORS in the init code

[Marc Zyngier]

Now that we have an infrastructure to handle hypercalls in the KVM
init code, let's implement HVC_GET_VECTORS there.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm64/kvm/hyp-init.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
index 948f331c7f32..2c7b86bb5483 100644
--- a/arch/arm64/kvm/hyp-init.S
+++ b/arch/arm64/kvm/hyp-init.S
@@ -124,7 +124,12 @@ __do_hyp_init:
 ENDPROC(__kvm_hyp_init)
 
 ENTRY(__kvm_handle_stub_hvc)
-	cmp	x0, #HVC_RESET_VECTORS
+	cmp	x0, #HVC_GET_VECTORS
+	b.ne	1f
+	mrs	x0, vbar_el2
+	b	exit
+
+1:	cmp	x0, #HVC_RESET_VECTORS
 	b.ne	1f
 	/*
 	 * Reset kvm back to the hyp stub.
-- 
2.11.0

[PATCH 04/20] arm64: KVM: Allow the main HYP code to use the init hyp stub implementation

[Marc Zyngier]

We now have a full hyp-stub implementation in the KVM init code,
but the main KVM code only supports HVC_GET_VECTORS, which is not
enough.

Instead of reinventing the wheel, let's reuse the init implementation
by branching to the idmap page when called with a hyp-stub hypercall.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm64/kvm/hyp/hyp-entry.S | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 5e9052f087f2..21eeb2552f33 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -87,10 +87,24 @@ alternative_endif
 	/* Here, we're pretty sure the host called HVC. */
 	ldp	x0, x1, [sp], #16
 
-	cmp	x0, #HVC_GET_VECTORS
-	b.ne	1f
-	mrs	x0, vbar_el2
-	b	2f
+	/* Check for a stub HVC call */
+	cmp	x0, #HVC_STUB_HCALL_NR
+	b.hs	1f
+
+	/*
+	 * Compute the idmap address of __kvm_handle_stub_hvc and
+	 * jump there. Since we use kimage_voffset, do not use the
+	 * HYP VA for __kvm_handle_stub_hvc, but the kernel VA instead
+	 * (by loading it from the constant pool).
+	 *
+	 * Preserve x0-x4, which may contain stub parameters.
+	 */
+	ldr	x5, =__kvm_handle_stub_hvc
+	ldr_l	x6, kimage_voffset
+
+	/* x5 = __pa(x5) */
+	sub	x5, x5, x6
+	br	x5
 
 1:
 	/*
@@ -99,7 +113,7 @@ alternative_endif
 	kern_hyp_va	x0
 	do_el2_call
 
-2:	eret
+	eret
 
 el1_trap:
 	/*
-- 
2.11.0

[PATCH 05/20] arm64: KVM: Convert __cpu_reset_hyp_mode to using __hyp_reset_vectors

[Marc Zyngier]

We are now able to use the hyp stub to reset HYP mode. Time to
kiss __kvm_hyp_reset goodbye, and use __hyp_reset_vectors.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm64/include/asm/kvm_asm.h  |  1 -
 arch/arm64/include/asm/kvm_host.h |  4 ++--
 arch/arm64/kvm/hyp-init.S         |  2 --
 arch/arm64/kvm/hyp/hyp-entry.S    | 15 ---------------
 4 files changed, 2 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index ec3553eb9349..3e242f6613b3 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -47,7 +47,6 @@ struct kvm_vcpu;
 
 extern char __kvm_hyp_init[];
 extern char __kvm_hyp_init_end[];
-extern char __kvm_hyp_reset[];
 
 extern char __kvm_hyp_vector[];
 
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index e5050388e062..2e493e9a671e 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -361,11 +361,11 @@ static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
 	__kvm_call_hyp((void *)pgd_ptr, hyp_stack_ptr, vector_ptr);
 }
 
-void __kvm_hyp_teardown(void);
 static inline void __cpu_reset_hyp_mode(unsigned long vector_ptr,
 					phys_addr_t phys_idmap_start)
 {
-	kvm_call_hyp(__kvm_hyp_teardown, phys_idmap_start);
+	extern void __hyp_reset_vectors(void);
+	__hyp_reset_vectors();
 }
 
 static inline void kvm_arch_hardware_unsetup(void) {}
diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
index 2c7b86bb5483..d12a232abd81 100644
--- a/arch/arm64/kvm/hyp-init.S
+++ b/arch/arm64/kvm/hyp-init.S
@@ -134,7 +134,6 @@ ENTRY(__kvm_handle_stub_hvc)
 	/*
 	 * Reset kvm back to the hyp stub.
 	 */
-ENTRY(__kvm_hyp_reset)
 	/* We're now in idmap, disable MMU */
 	mrs	x0, sctlr_el2
 	ldr	x1, =SCTLR_ELx_FLAGS
@@ -151,7 +150,6 @@ ENTRY(__kvm_hyp_reset)
 
 exit:
 	eret
-ENDPROC(__kvm_hyp_reset)
 ENDPROC(__kvm_handle_stub_hvc)
 
 	.ltorg
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 21eeb2552f33..1277f81b63b7 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -53,21 +53,6 @@ ENTRY(__vhe_hyp_call)
 	ret
 ENDPROC(__vhe_hyp_call)
 
-/*
- * Compute the idmap address of __kvm_hyp_reset based on the idmap
- * start passed as a parameter, and jump there.
- *
- * x0: HYP phys_idmap_start
- */
-ENTRY(__kvm_hyp_teardown)
-	mov	x4, x0
-	adr_l	x3, __kvm_hyp_reset
-
-	/* insert __kvm_hyp_reset()s offset into phys_idmap_start */
-	bfi	x4, x3, #0, #PAGE_SHIFT
-	br	x4
-ENDPROC(__kvm_hyp_teardown)
-	
 el1_sync:				// Guest trapped into EL2
 	stp	x0, x1, [sp, #-16]!
 
-- 
2.11.0

[PATCH 06/20] arm64: KVM: Implement HVC_SOFT_RESTART in the init code

[Marc Zyngier]

Another missing stub hypercall is HVC_SOFT_RESTART. It turns out
that it is pretty easy to implement in terms of HVC_RESET_VECTORS
(since it needs to turn the MMU off).

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm64/kvm/hyp-init.S | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
index d12a232abd81..586a35b4aaf3 100644
--- a/arch/arm64/kvm/hyp-init.S
+++ b/arch/arm64/kvm/hyp-init.S
@@ -129,21 +129,36 @@ ENTRY(__kvm_handle_stub_hvc)
 	mrs	x0, vbar_el2
 	b	exit
 
+1:	cmp	x0, #HVC_SOFT_RESTART
+	b.ne	1f
+
+	/* This is where we're about to jump, staying at EL2 */
+	msr	elr_el2, x1
+	mov	x0, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT | PSR_MODE_EL2h)
+	msr	spsr_el2, x0
+
+	/* Shuffle the arguments, and don't come back */
+	mov	x0, x2
+	mov	x1, x3
+	mov	x2, x4
+	b	reset
+
 1:	cmp	x0, #HVC_RESET_VECTORS
 	b.ne	1f
+reset:
 	/*
-	 * Reset kvm back to the hyp stub.
+	 * Reset kvm back to the hyp stub. Do not clobber x0-x4 in
+	 * case we coming via HVC_SOFT_RESTART.
 	 */
-	/* We're now in idmap, disable MMU */
-	mrs	x0, sctlr_el2
-	ldr	x1, =SCTLR_ELx_FLAGS
-	bic	x0, x0, x1		// Clear SCTL_M and etc
-	msr	sctlr_el2, x0
+	mrs	x5, sctlr_el2
+	ldr	x6, =SCTLR_ELx_FLAGS
+	bic	x5, x5, x6		// Clear SCTL_M and etc
+	msr	sctlr_el2, x5
 	isb
 
 	/* Install stub vectors */
-	adr_l	x0, __hyp_stub_vectors
-	msr	vbar_el2, x0
+	adr_l	x5, __hyp_stub_vectors
+	msr	vbar_el2, x5
 	b	exit
 
 1:	mov	x0, #-1
-- 
2.11.0

[PATCH 07/20] ARM: hyp-stub: improve ABI

[Marc Zyngier]

From: Russell King <rmk+kernel@armlinux.org.uk>

Improve the hyp-stub ABI to allow it to do more than just get/set the
vectors.  We follow the example in ARM64, where r0 is used as an opcode
with the other registers as an argument.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 arch/arm/kernel/hyp-stub.S | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index 15d073ae5da2..f3e9ba5fb642 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -22,6 +22,9 @@
 #include <asm/assembler.h>
 #include <asm/virt.h>
 
+#define HVC_GET_VECTORS 0
+#define HVC_SET_VECTORS 1
+
 #ifndef ZIMAGE
 /*
  * For the kernel proper, we need to find out the CPU boot mode long after
@@ -202,9 +205,19 @@ ARM_BE8(orr	r7, r7, #(1 << 25))     @ HSCTLR.EE
 ENDPROC(__hyp_stub_install_secondary)
 
 __hyp_stub_do_trap:
-	cmp	r0, #-1
-	mrceq	p15, 4, r0, c12, c0, 0	@ get HVBAR
-	mcrne	p15, 4, r0, c12, c0, 0	@ set HVBAR
+	teq	r0, #HVC_GET_VECTORS
+	bne	1f
+	mrc	p15, 4, r0, c12, c0, 0	@ get HVBAR
+	b	__hyp_stub_exit
+
+1:	teq	r0, #HVC_SET_VECTORS
+	bne	1f
+	mcr	p15, 4, r1, c12, c0, 0	@ set HVBAR
+	b	__hyp_stub_exit
+
+1:	mov	r0, #-1
+
+__hyp_stub_exit:
 	__ERET
 ENDPROC(__hyp_stub_do_trap)
 
@@ -231,10 +244,14 @@ ENDPROC(__hyp_stub_do_trap)
  * initialisation entry point.
  */
 ENTRY(__hyp_get_vectors)
-	mov	r0, #-1
+	mov	r0, #HVC_GET_VECTORS
+	__HVC(0)
+	ret	lr
 ENDPROC(__hyp_get_vectors)
-	@ fall through
+
 ENTRY(__hyp_set_vectors)
+	mov	r1, r0
+	mov	r0, #HVC_SET_VECTORS
 	__HVC(0)
 	ret	lr
 ENDPROC(__hyp_set_vectors)
-- 
2.11.0

[PATCH 08/20] ARM: soft-reboot into same mode that we entered the kernel

[Marc Zyngier]

From: Russell King <rmk+kernel@armlinux.org.uk>

When we soft-reboot (eg, kexec) from one kernel into the next, we need
to ensure that we enter the new kernel in the same processor mode as
when we were entered, so that (eg) the new kernel can install its own
hypervisor - the old kernel's hypervisor will have been overwritten.

In order to do this, we need to pass a flag to cpu_reset() so it knows
what to do, and we need to modify the kernel's own hypervisor stub to
allow it to handle a soft-reboot.

As we are always guaranteed to install our own hypervisor if we're
entered in HYP32 mode, and KVM will have moved itself out of the way
on kexec/normal reboot, we can assume that our hypervisor is in place
when we want to kexec, so changing our hypervisor API should not be a
problem.

Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 arch/arm/include/asm/proc-fns.h |  4 ++--
 arch/arm/kernel/hyp-stub.S      | 13 +++++++++++++
 arch/arm/kernel/reboot.c        |  7 +++++--
 arch/arm/mm/proc-v7.S           | 12 ++++++++----
 4 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/arch/arm/include/asm/proc-fns.h b/arch/arm/include/asm/proc-fns.h
index 8877ad5ffe10..f2e1af45bd6f 100644
--- a/arch/arm/include/asm/proc-fns.h
+++ b/arch/arm/include/asm/proc-fns.h
@@ -43,7 +43,7 @@ extern struct processor {
 	/*
 	 * Special stuff for a reset
 	 */
-	void (*reset)(unsigned long addr) __attribute__((noreturn));
+	void (*reset)(unsigned long addr, bool hvc) __attribute__((noreturn));
 	/*
 	 * Idle the processor
 	 */
@@ -88,7 +88,7 @@ extern void cpu_set_pte_ext(pte_t *ptep, pte_t pte);
 #else
 extern void cpu_set_pte_ext(pte_t *ptep, pte_t pte, unsigned int ext);
 #endif
-extern void cpu_reset(unsigned long addr) __attribute__((noreturn));
+extern void cpu_reset(unsigned long addr, bool hvc) __attribute__((noreturn));
 
 /* These three are private to arch/arm/kernel/suspend.c */
 extern void cpu_do_suspend(void *);
diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index f3e9ba5fb642..82915231c6f8 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -24,6 +24,7 @@
 
 #define HVC_GET_VECTORS 0
 #define HVC_SET_VECTORS 1
+#define HVC_SOFT_RESTART 2
 
 #ifndef ZIMAGE
 /*
@@ -215,6 +216,10 @@ __hyp_stub_do_trap:
 	mcr	p15, 4, r1, c12, c0, 0	@ set HVBAR
 	b	__hyp_stub_exit
 
+1:	teq	r0, #HVC_SOFT_RESTART
+	bne	1f
+	bx	r3
+
 1:	mov	r0, #-1
 
 __hyp_stub_exit:
@@ -256,6 +261,14 @@ ENTRY(__hyp_set_vectors)
 	ret	lr
 ENDPROC(__hyp_set_vectors)
 
+ENTRY(__hyp_soft_restart)
+	mov	r3, r0
+	mov	r0, #HVC_SOFT_RESTART
+	__HVC(0)
+	mov	r0, r3
+	ret	lr
+ENDPROC(__hyp_soft_restart)
+
 #ifndef ZIMAGE
 .align 2
 .L__boot_cpu_mode_offset:
diff --git a/arch/arm/kernel/reboot.c b/arch/arm/kernel/reboot.c
index 3fa867a2aae6..3b2aa9a9fe26 100644
--- a/arch/arm/kernel/reboot.c
+++ b/arch/arm/kernel/reboot.c
@@ -12,10 +12,11 @@
 
 #include <asm/cacheflush.h>
 #include <asm/idmap.h>
+#include <asm/virt.h>
 
 #include "reboot.h"
 
-typedef void (*phys_reset_t)(unsigned long);
+typedef void (*phys_reset_t)(unsigned long, bool);
 
 /*
  * Function pointers to optional machine specific functions
@@ -51,7 +52,9 @@ static void __soft_restart(void *addr)
 
 	/* Switch to the identity mapping. */
 	phys_reset = (phys_reset_t)virt_to_idmap(cpu_reset);
-	phys_reset((unsigned long)addr);
+
+	/* original stub should be restored by kvm */
+	phys_reset((unsigned long)addr, is_hyp_mode_available());
 
 	/* Should never get here. */
 	BUG();
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index d00d52c9de3e..1846ca4255d0 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -53,11 +53,15 @@ ENDPROC(cpu_v7_proc_fin)
 	.align	5
 	.pushsection	.idmap.text, "ax"
 ENTRY(cpu_v7_reset)
-	mrc	p15, 0, r1, c1, c0, 0		@ ctrl register
-	bic	r1, r1, #0x1			@ ...............m
- THUMB(	bic	r1, r1, #1 << 30 )		@ SCTLR.TE (Thumb exceptions)
-	mcr	p15, 0, r1, c1, c0, 0		@ disable MMU
+	mrc	p15, 0, r2, c1, c0, 0		@ ctrl register
+	bic	r2, r2, #0x1			@ ...............m
+ THUMB(	bic	r2, r2, #1 << 30 )		@ SCTLR.TE (Thumb exceptions)
+	mcr	p15, 0, r2, c1, c0, 0		@ disable MMU
 	isb
+#ifdef CONFIG_ARM_VIRT_EXT
+	teq	r1, #0
+	bne	__hyp_soft_restart
+#endif
 	bx	r0
 ENDPROC(cpu_v7_reset)
 	.popsection
-- 
2.11.0

[PATCH 09/20] ARM: KVM: Convert KVM to use HVC_GET_VECTORS

[Marc Zyngier]

The conversion of the HYP stub ABI to something similar to arm64
left the KVM code broken, as it doesn't know about the new
stub numbering. Let's move the various #defines to virt.h, and
let KVM use HVC_GET_VECTORS.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/include/asm/virt.h  | 8 ++++++++
 arch/arm/kernel/hyp-stub.S   | 4 ----
 arch/arm/kvm/hyp/hyp-entry.S | 2 +-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/arm/include/asm/virt.h b/arch/arm/include/asm/virt.h
index 6dae1956c74d..4ea16fcaf2ed 100644
--- a/arch/arm/include/asm/virt.h
+++ b/arch/arm/include/asm/virt.h
@@ -94,6 +94,14 @@ extern char __hyp_text_start[];
 extern char __hyp_text_end[];
 #endif
 
+#else
+
+/* Only assembly code should need those */
+
+#define HVC_GET_VECTORS 0
+#define HVC_SET_VECTORS 1
+#define HVC_SOFT_RESTART 2
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* ! VIRT_H */
diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index 82915231c6f8..8301db963d83 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -22,10 +22,6 @@
 #include <asm/assembler.h>
 #include <asm/virt.h>
 
-#define HVC_GET_VECTORS 0
-#define HVC_SET_VECTORS 1
-#define HVC_SOFT_RESTART 2
-
 #ifndef ZIMAGE
 /*
  * For the kernel proper, we need to find out the CPU boot mode long after
diff --git a/arch/arm/kvm/hyp/hyp-entry.S b/arch/arm/kvm/hyp/hyp-entry.S
index 96beb53934c9..1f8db7d21fc5 100644
--- a/arch/arm/kvm/hyp/hyp-entry.S
+++ b/arch/arm/kvm/hyp/hyp-entry.S
@@ -127,7 +127,7 @@ hyp_hvc:
 	pop	{r0, r1, r2}
 
 	/* Check for __hyp_get_vectors */
-	cmp	r0, #-1
+	cmp	r0, #HVC_GET_VECTORS
 	mrceq	p15, 4, r0, c12, c0, 0	@ get HVBAR
 	beq	1f
 
-- 
2.11.0

[PATCH 10/20] ARM: hyp-stub: Use r1 for the soft-restart address

[Marc Zyngier]

It is not really obvious why the restart address should be in r3
when communicated to the hyp-stub. r1 should be perfectly adequate,
and consistent with the rest of the code.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kernel/hyp-stub.S | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index 8301db963d83..8fa521bd63d2 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -214,7 +214,7 @@ __hyp_stub_do_trap:
 
 1:	teq	r0, #HVC_SOFT_RESTART
 	bne	1f
-	bx	r3
+	bx	r1
 
 1:	mov	r0, #-1
 
@@ -258,10 +258,8 @@ ENTRY(__hyp_set_vectors)
 ENDPROC(__hyp_set_vectors)
 
 ENTRY(__hyp_soft_restart)
-	mov	r3, r0
 	mov	r0, #HVC_SOFT_RESTART
 	__HVC(0)
-	mov	r0, r3
 	ret	lr
 ENDPROC(__hyp_soft_restart)
 
-- 
2.11.0

[PATCH 10/20] ARM: hyp-stub: Use r1 for the soft-restart address

[Ard Biesheuvel]

On 17 February 2017 at 15:44, Marc Zyngier <marc.zyngier@arm.com> wrote:
> It is not really obvious why the restart address should be in r3
> when communicated to the hyp-stub. r1 should be perfectly adequate,
> and consistent with the rest of the code.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm/kernel/hyp-stub.S | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> index 8301db963d83..8fa521bd63d2 100644
> --- a/arch/arm/kernel/hyp-stub.S
> +++ b/arch/arm/kernel/hyp-stub.S
> @@ -214,7 +214,7 @@ __hyp_stub_do_trap:
>
>  1:     teq     r0, #HVC_SOFT_RESTART
>         bne     1f
> -       bx      r3
> +       bx      r1
>
>  1:     mov     r0, #-1
>
> @@ -258,10 +258,8 @@ ENTRY(__hyp_set_vectors)
>  ENDPROC(__hyp_set_vectors)
>
>  ENTRY(__hyp_soft_restart)
> -       mov     r3, r0
>         mov     r0, #HVC_SOFT_RESTART
>         __HVC(0)
> -       mov     r0, r3
>         ret     lr
>  ENDPROC(__hyp_soft_restart)
>

/me confused. How does the address end up in r1?

[PATCH 10/20] ARM: hyp-stub: Use r1 for the soft-restart address

[Marc Zyngier]

On Sun, 19 Feb 2017 08:22:23 +0000
Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> On 17 February 2017 at 15:44, Marc Zyngier <marc.zyngier@arm.com> wrote:
> > It is not really obvious why the restart address should be in r3
> > when communicated to the hyp-stub. r1 should be perfectly adequate,
> > and consistent with the rest of the code.
> >
> > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> > ---
> >  arch/arm/kernel/hyp-stub.S | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> > index 8301db963d83..8fa521bd63d2 100644
> > --- a/arch/arm/kernel/hyp-stub.S
> > +++ b/arch/arm/kernel/hyp-stub.S
> > @@ -214,7 +214,7 @@ __hyp_stub_do_trap:
> >
> >  1:     teq     r0, #HVC_SOFT_RESTART
> >         bne     1f
> > -       bx      r3
> > +       bx      r1
> >
> >  1:     mov     r0, #-1
> >
> > @@ -258,10 +258,8 @@ ENTRY(__hyp_set_vectors)
> >  ENDPROC(__hyp_set_vectors)
> >
> >  ENTRY(__hyp_soft_restart)
> > -       mov     r3, r0
> >         mov     r0, #HVC_SOFT_RESTART
> >         __HVC(0)
> > -       mov     r0, r3
> >         ret     lr
> >  ENDPROC(__hyp_soft_restart)
> >  
> 
> /me confused. How does the address end up in r1?

I'm now very confused too. I just gave it another go on my A7 platform,
and it restarted just right, even if there is obviously junk in r1.
Guess I'm just bloody lucky.

Thanks for the heads up, I'll fix that for v2.

	M.
-- 
Without deviation from the norm, progress is not possible.

[PATCH 11/20] ARM: Expose the VA/IDMAP offset

[Marc Zyngier]

The KVM code needs to be able to compute the address of
symbols in its idmap page (the equivalent of a virt_to_idmap()
call). Unfortunately, virt_to_idmap is slightly complicated,
depending on the use of arch_phys_to_idmap_offset or not, and
none of that is readily available at HYP.

Instead, expose a single kimage_voffset variable which contains the
offset between a kernel VA and its idmap address, enabling the
VA->IDMAP conversion. This allows the KVM code to behave similarily
to its arm64 counterpart.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/mm/mmu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 4001dd15818d..d9bb3ae876ad 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -87,6 +87,8 @@ struct cachepolicy {
 #define s2_policy(policy)	0
 #endif
 
+unsigned long kimage_voffset __ro_after_init;
+
 static struct cachepolicy cache_policies[] __initdata = {
 	{
 		.policy		= "uncached",
@@ -1654,4 +1656,7 @@ void __init paging_init(const struct machine_desc *mdesc)
 
 	empty_zero_page = virt_to_page(zero_page);
 	__flush_dcache_page(NULL, empty_zero_page);
+
+	/* Compute the virt/idmap offset, mostly for the sake of KVM */
+	kimage_voffset = (unsigned long)&kimage_voffset - virt_to_idmap(&kimage_voffset);
 }
-- 
2.11.0

[PATCH 12/20] ARM: hyp-stub: Implement HVC_RESET_VECTORS stub hypercall

[Marc Zyngier]

Let's define a new stub hypercall that resets the HYP configuration
to its default: hyp-stub vectors, and MMU disabled.

Of course, for the hyp-stub itself, this is a trivial no-op.
Hypervisors will have a bit more work to do.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/include/asm/virt.h |  3 +++
 arch/arm/kernel/hyp-stub.S  | 11 ++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/virt.h b/arch/arm/include/asm/virt.h
index 4ea16fcaf2ed..5186718aab68 100644
--- a/arch/arm/include/asm/virt.h
+++ b/arch/arm/include/asm/virt.h
@@ -101,6 +101,9 @@ extern char __hyp_text_end[];
 #define HVC_GET_VECTORS 0
 #define HVC_SET_VECTORS 1
 #define HVC_SOFT_RESTART 2
+#define HVC_RESET_VECTORS 3
+
+#define HVC_STUB_HCALL_NR 4
 
 #endif /* __ASSEMBLY__ */
 
diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index 8fa521bd63d2..cf6d801f89e8 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -216,7 +216,10 @@ __hyp_stub_do_trap:
 	bne	1f
 	bx	r1
 
-1:	mov	r0, #-1
+1:	teq	r0, #HVC_RESET_VECTORS
+	beq	__hyp_stub_exit
+
+	mov	r0, #-1
 
 __hyp_stub_exit:
 	__ERET
@@ -263,6 +266,12 @@ ENTRY(__hyp_soft_restart)
 	ret	lr
 ENDPROC(__hyp_soft_restart)
 
+ENTRY(__hyp_reset_vectors)
+	mov	r0, #HVC_RESET_VECTORS
+	__HVC(0)
+	ret	lr
+ENDPROC(__hyp_reset_vectors)
+
 #ifndef ZIMAGE
 .align 2
 .L__boot_cpu_mode_offset:
-- 
2.11.0

[PATCH 13/20] ARM: KVM: Implement HVC_RESET_VECTORS stub hypercall

[Marc Zyngier]

In order to restore HYP mode to its original condition, KVM currently
implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
defined API, it becomes necessary to implement HVC_RESET_VECTORS.

This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
code, which so far lacked any form of hypercall support.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kernel/hyp-stub.S |  1 +
 arch/arm/kvm/init.S        | 37 +++++++++++++++++++++++++++++++------
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index cf6d801f89e8..171a09cdf6b3 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -280,6 +280,7 @@ ENDPROC(__hyp_reset_vectors)
 
 .align 5
 __hyp_stub_vectors:
+.global __hyp_stub_vectors
 __hyp_stub_reset:	W(b)	.
 __hyp_stub_und:		W(b)	.
 __hyp_stub_svc:		W(b)	.
diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
index bf89c919efc1..b0138118fac4 100644
--- a/arch/arm/kvm/init.S
+++ b/arch/arm/kvm/init.S
@@ -23,6 +23,7 @@
 #include <asm/kvm_asm.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_mmu.h>
+#include <asm/virt.h>
 
 /********************************************************************
  * Hypervisor initialization
@@ -39,6 +40,10 @@
  * - Setup the page tables
  * - Enable the MMU
  * - Profit! (or eret, if you only care about the code).
+ *
+ * Another possibility is to get a HYP stub hypercall.
+ * We discriminate between the two by checking if r0 contains a value
+ * that is less than HVC_STUB_HCALL_NR.
  */
 
 	.text
@@ -58,6 +63,10 @@ __kvm_hyp_init:
 	W(b)	.
 
 __do_hyp_init:
+	@ Check for a stub hypercall
+	cmp	r0, #HVC_STUB_HCALL_NR
+	blo	__kvm_handle_stub_hvc
+
 	@ Set stack pointer
 	mov	sp, r0
 
@@ -112,22 +121,38 @@ __do_hyp_init:
 
 	eret
 
-	@ r0 : stub vectors address
+ENTRY(__kvm_handle_stub_hvc)
+	cmp	r0, #HVC_RESET_VECTORS
+	bne	1f
 ENTRY(__kvm_hyp_reset)
 	/* We're now in idmap, disable MMU */
 	mrc	p15, 4, r1, c1, c0, 0	@ HSCTLR
-	ldr	r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
-	bic	r1, r1, r2
+	ldr	r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
+	bic	r1, r1, r0
 	mcr	p15, 4, r1, c1, c0, 0	@ HSCTLR
 
-	/* Install stub vectors */
-	mcr	p15, 4, r0, c12, c0, 0	@ HVBAR
-	isb
+	/*
+	 * Install stub vectors. We cannot use 'adr' to get to the
+	 * stub vectors, hence having to play the VA->PA game.
+	 */
+	adr	r0, .L__va2pa	@ PA
+	ldr	r1, [r0]	@ VA
+	sub	r0, r0, r1	@ PA - VA
+	ldr	r1, =__hyp_stub_vectors
+	add	r1, r1, r0
+	mcr	p15, 4, r1, c12, c0, 0	@ HVBAR
+	b	exit
+
+1:	mov	r0, #-1
 
+exit:
 	eret
+ENDPROC(__kvm_handle_stub_hvc)
 ENDPROC(__kvm_hyp_reset)
 
 	.ltorg
+.L__va2pa:
+	.word	.
 
 	.globl __kvm_hyp_init_end
 __kvm_hyp_init_end:
-- 
2.11.0

[PATCH 13/20] ARM: KVM: Implement HVC_RESET_VECTORS stub hypercall

[Ard Biesheuvel]

On 17 February 2017 at 15:44, Marc Zyngier <marc.zyngier@arm.com> wrote:
> In order to restore HYP mode to its original condition, KVM currently
> implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
> defined API, it becomes necessary to implement HVC_RESET_VECTORS.
>
> This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
> code, which so far lacked any form of hypercall support.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm/kernel/hyp-stub.S |  1 +
>  arch/arm/kvm/init.S        | 37 +++++++++++++++++++++++++++++++------
>  2 files changed, 32 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> index cf6d801f89e8..171a09cdf6b3 100644
> --- a/arch/arm/kernel/hyp-stub.S
> +++ b/arch/arm/kernel/hyp-stub.S
> @@ -280,6 +280,7 @@ ENDPROC(__hyp_reset_vectors)
>
>  .align 5
>  __hyp_stub_vectors:
> +.global __hyp_stub_vectors
>  __hyp_stub_reset:      W(b)    .
>  __hyp_stub_und:                W(b)    .
>  __hyp_stub_svc:                W(b)    .
> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
> index bf89c919efc1..b0138118fac4 100644
> --- a/arch/arm/kvm/init.S
> +++ b/arch/arm/kvm/init.S
> @@ -23,6 +23,7 @@
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_mmu.h>
> +#include <asm/virt.h>
>
>  /********************************************************************
>   * Hypervisor initialization
> @@ -39,6 +40,10 @@
>   * - Setup the page tables
>   * - Enable the MMU
>   * - Profit! (or eret, if you only care about the code).
> + *
> + * Another possibility is to get a HYP stub hypercall.
> + * We discriminate between the two by checking if r0 contains a value
> + * that is less than HVC_STUB_HCALL_NR.
>   */
>
>         .text
> @@ -58,6 +63,10 @@ __kvm_hyp_init:
>         W(b)    .
>
>  __do_hyp_init:
> +       @ Check for a stub hypercall
> +       cmp     r0, #HVC_STUB_HCALL_NR
> +       blo     __kvm_handle_stub_hvc
> +
>         @ Set stack pointer
>         mov     sp, r0
>
> @@ -112,22 +121,38 @@ __do_hyp_init:
>
>         eret
>
> -       @ r0 : stub vectors address
> +ENTRY(__kvm_handle_stub_hvc)
> +       cmp     r0, #HVC_RESET_VECTORS
> +       bne     1f
>  ENTRY(__kvm_hyp_reset)
>         /* We're now in idmap, disable MMU */
>         mrc     p15, 4, r1, c1, c0, 0   @ HSCTLR
> -       ldr     r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> -       bic     r1, r1, r2
> +       ldr     r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> +       bic     r1, r1, r0
>         mcr     p15, 4, r1, c1, c0, 0   @ HSCTLR
>
> -       /* Install stub vectors */
> -       mcr     p15, 4, r0, c12, c0, 0  @ HVBAR
> -       isb
> +       /*
> +        * Install stub vectors. We cannot use 'adr' to get to the
> +        * stub vectors, hence having to play the VA->PA game.
> +        */
> +       adr     r0, .L__va2pa   @ PA
> +       ldr     r1, [r0]        @ VA
> +       sub     r0, r0, r1      @ PA - VA
> +       ldr     r1, =__hyp_stub_vectors

Since we're guaranteed to be on v7, how about something like
0:adr r0, 0b
  movw r1, #:lower16:__hyp_stub_vectors - 0b
  movt r1, #:upper16:__hyp_stub_vectors - 0b

> +       add     r1, r1, r0
> +       mcr     p15, 4, r1, c12, c0, 0  @ HVBAR
> +       b       exit
> +
> +1:     mov     r0, #-1
>
> +exit:
>         eret
> +ENDPROC(__kvm_handle_stub_hvc)
>  ENDPROC(__kvm_hyp_reset)
>
>         .ltorg
> +.L__va2pa:
> +       .word   .
>
>         .globl __kvm_hyp_init_end
>  __kvm_hyp_init_end:
> --
> 2.11.0
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 13/20] ARM: KVM: Implement HVC_RESET_VECTORS stub hypercall

[Marc Zyngier]

On Sun, 19 Feb 2017 08:07:22 +0000
Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:

> On 17 February 2017 at 15:44, Marc Zyngier <marc.zyngier@arm.com> wrote:
> > In order to restore HYP mode to its original condition, KVM currently
> > implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
> > defined API, it becomes necessary to implement HVC_RESET_VECTORS.
> >
> > This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
> > code, which so far lacked any form of hypercall support.
> >
> > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> > ---
> >  arch/arm/kernel/hyp-stub.S |  1 +
> >  arch/arm/kvm/init.S        | 37 +++++++++++++++++++++++++++++++------
> >  2 files changed, 32 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> > index cf6d801f89e8..171a09cdf6b3 100644
> > --- a/arch/arm/kernel/hyp-stub.S
> > +++ b/arch/arm/kernel/hyp-stub.S
> > @@ -280,6 +280,7 @@ ENDPROC(__hyp_reset_vectors)
> >
> >  .align 5
> >  __hyp_stub_vectors:
> > +.global __hyp_stub_vectors
> >  __hyp_stub_reset:      W(b)    .
> >  __hyp_stub_und:                W(b)    .
> >  __hyp_stub_svc:                W(b)    .
> > diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
> > index bf89c919efc1..b0138118fac4 100644
> > --- a/arch/arm/kvm/init.S
> > +++ b/arch/arm/kvm/init.S
> > @@ -23,6 +23,7 @@
> >  #include <asm/kvm_asm.h>
> >  #include <asm/kvm_arm.h>
> >  #include <asm/kvm_mmu.h>
> > +#include <asm/virt.h>
> >
> >  /********************************************************************
> >   * Hypervisor initialization
> > @@ -39,6 +40,10 @@
> >   * - Setup the page tables
> >   * - Enable the MMU
> >   * - Profit! (or eret, if you only care about the code).
> > + *
> > + * Another possibility is to get a HYP stub hypercall.
> > + * We discriminate between the two by checking if r0 contains a value
> > + * that is less than HVC_STUB_HCALL_NR.
> >   */
> >
> >         .text
> > @@ -58,6 +63,10 @@ __kvm_hyp_init:
> >         W(b)    .
> >
> >  __do_hyp_init:
> > +       @ Check for a stub hypercall
> > +       cmp     r0, #HVC_STUB_HCALL_NR
> > +       blo     __kvm_handle_stub_hvc
> > +
> >         @ Set stack pointer
> >         mov     sp, r0
> >
> > @@ -112,22 +121,38 @@ __do_hyp_init:
> >
> >         eret
> >
> > -       @ r0 : stub vectors address
> > +ENTRY(__kvm_handle_stub_hvc)
> > +       cmp     r0, #HVC_RESET_VECTORS
> > +       bne     1f
> >  ENTRY(__kvm_hyp_reset)
> >         /* We're now in idmap, disable MMU */
> >         mrc     p15, 4, r1, c1, c0, 0   @ HSCTLR
> > -       ldr     r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> > -       bic     r1, r1, r2
> > +       ldr     r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> > +       bic     r1, r1, r0
> >         mcr     p15, 4, r1, c1, c0, 0   @ HSCTLR
> >
> > -       /* Install stub vectors */
> > -       mcr     p15, 4, r0, c12, c0, 0  @ HVBAR
> > -       isb
> > +       /*
> > +        * Install stub vectors. We cannot use 'adr' to get to the
> > +        * stub vectors, hence having to play the VA->PA game.
> > +        */
> > +       adr     r0, .L__va2pa   @ PA
> > +       ldr     r1, [r0]        @ VA
> > +       sub     r0, r0, r1      @ PA - VA
> > +       ldr     r1, =__hyp_stub_vectors  
> 
> Since we're guaranteed to be on v7, how about something like
> 0:adr r0, 0b
>   movw r1, #:lower16:__hyp_stub_vectors - 0b
>   movt r1, #:upper16:__hyp_stub_vectors - 0b

Ah, very nice! It hurts my brain, but it is very nice indeed! I'll
borrow that for v2.

Thanks,

	M.
-- 
Without deviation from the norm, progress is not possible.

[PATCH 13/20] ARM: KVM: Implement HVC_RESET_VECTORS stub hypercall

[Ard Biesheuvel]

On 17 February 2017 at 15:44, Marc Zyngier <marc.zyngier@arm.com> wrote:
> In order to restore HYP mode to its original condition, KVM currently
> implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
> defined API, it becomes necessary to implement HVC_RESET_VECTORS.
>
> This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
> code, which so far lacked any form of hypercall support.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm/kernel/hyp-stub.S |  1 +
>  arch/arm/kvm/init.S        | 37 +++++++++++++++++++++++++++++++------
>  2 files changed, 32 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> index cf6d801f89e8..171a09cdf6b3 100644
> --- a/arch/arm/kernel/hyp-stub.S
> +++ b/arch/arm/kernel/hyp-stub.S
> @@ -280,6 +280,7 @@ ENDPROC(__hyp_reset_vectors)
>
>  .align 5
>  __hyp_stub_vectors:
> +.global __hyp_stub_vectors

Oh, and (nit:) perhaps use

ENTRY(__hyp_stub_vectors)

here?

>  __hyp_stub_reset:      W(b)    .
>  __hyp_stub_und:                W(b)    .
>  __hyp_stub_svc:                W(b)    .
> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
> index bf89c919efc1..b0138118fac4 100644
> --- a/arch/arm/kvm/init.S
> +++ b/arch/arm/kvm/init.S
> @@ -23,6 +23,7 @@
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_mmu.h>
> +#include <asm/virt.h>
>
>  /********************************************************************
>   * Hypervisor initialization
> @@ -39,6 +40,10 @@
>   * - Setup the page tables
>   * - Enable the MMU
>   * - Profit! (or eret, if you only care about the code).
> + *
> + * Another possibility is to get a HYP stub hypercall.
> + * We discriminate between the two by checking if r0 contains a value
> + * that is less than HVC_STUB_HCALL_NR.
>   */
>
>         .text
> @@ -58,6 +63,10 @@ __kvm_hyp_init:
>         W(b)    .
>
>  __do_hyp_init:
> +       @ Check for a stub hypercall
> +       cmp     r0, #HVC_STUB_HCALL_NR
> +       blo     __kvm_handle_stub_hvc
> +
>         @ Set stack pointer
>         mov     sp, r0
>
> @@ -112,22 +121,38 @@ __do_hyp_init:
>
>         eret
>
> -       @ r0 : stub vectors address
> +ENTRY(__kvm_handle_stub_hvc)
> +       cmp     r0, #HVC_RESET_VECTORS
> +       bne     1f
>  ENTRY(__kvm_hyp_reset)
>         /* We're now in idmap, disable MMU */
>         mrc     p15, 4, r1, c1, c0, 0   @ HSCTLR
> -       ldr     r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> -       bic     r1, r1, r2
> +       ldr     r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> +       bic     r1, r1, r0
>         mcr     p15, 4, r1, c1, c0, 0   @ HSCTLR
>
> -       /* Install stub vectors */
> -       mcr     p15, 4, r0, c12, c0, 0  @ HVBAR
> -       isb
> +       /*
> +        * Install stub vectors. We cannot use 'adr' to get to the
> +        * stub vectors, hence having to play the VA->PA game.
> +        */
> +       adr     r0, .L__va2pa   @ PA
> +       ldr     r1, [r0]        @ VA
> +       sub     r0, r0, r1      @ PA - VA
> +       ldr     r1, =__hyp_stub_vectors
> +       add     r1, r1, r0
> +       mcr     p15, 4, r1, c12, c0, 0  @ HVBAR
> +       b       exit
> +
> +1:     mov     r0, #-1
>
> +exit:
>         eret
> +ENDPROC(__kvm_handle_stub_hvc)
>  ENDPROC(__kvm_hyp_reset)
>
>         .ltorg
> +.L__va2pa:
> +       .word   .
>
>         .globl __kvm_hyp_init_end
>  __kvm_hyp_init_end:
> --
> 2.11.0
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 14/20] ARM: KVM: Implement HVC_GET_VECTORS in the init code

[Marc Zyngier]

Now that we have an infrastructure to handle hypercalls in the KVM
init code, let's implement HVC_GET_VECTORS there.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kvm/init.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
index b0138118fac4..438b148d47fd 100644
--- a/arch/arm/kvm/init.S
+++ b/arch/arm/kvm/init.S
@@ -122,7 +122,12 @@ __do_hyp_init:
 	eret
 
 ENTRY(__kvm_handle_stub_hvc)
-	cmp	r0, #HVC_RESET_VECTORS
+	cmp	r0, #HVC_GET_VECTORS
+	bne	1f
+	mrc	p15, 4, r0, c12, c0, 0	@ get HVBAR
+	b	exit
+
+1:	cmp	r0, #HVC_RESET_VECTORS
 	bne	1f
 ENTRY(__kvm_hyp_reset)
 	/* We're now in idmap, disable MMU */
-- 
2.11.0

[PATCH 15/20] ARM: KVM: Allow the main HYP code to use the init hyp stub implementation

[Marc Zyngier]

We now have a full hyp-stub implementation in the KVM init code,
but the main KVM code only supports HVC_GET_VECTORS, which is not
enough.

Instead of reinventing the wheel, let's reuse the init implementation
by branching to the idmap page when called with a hyp-stub hypercall.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kvm/hyp/hyp-entry.S | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kvm/hyp/hyp-entry.S b/arch/arm/kvm/hyp/hyp-entry.S
index 1f8db7d21fc5..a35baa81fd23 100644
--- a/arch/arm/kvm/hyp/hyp-entry.S
+++ b/arch/arm/kvm/hyp/hyp-entry.S
@@ -126,11 +126,30 @@ hyp_hvc:
 	 */
 	pop	{r0, r1, r2}
 
-	/* Check for __hyp_get_vectors */
-	cmp	r0, #HVC_GET_VECTORS
-	mrceq	p15, 4, r0, c12, c0, 0	@ get HVBAR
-	beq	1f
+	/*
+	 * Check if we have a kernel function, which is guaranteed to be
+	 * bigger than the maximum hyp stub hypercall
+	 */
+	cmp	r0, #HVC_STUB_HCALL_NR
+	bhs	1f
 
+	/*
+	 * Not a kernel function, treat it as a stub hypercall.
+	 * Compute the physical address for __kvm_handle_stub_hvc
+	 * (as the code lives in the idmaped page) and branch there.
+	 * We hijack ip (r12) as a tmp register.
+	 */
+	push	{r1}
+	ldr	r1, =kimage_voffset
+	ldr	r1, [r1]
+	ldr	ip, =__kvm_handle_stub_hvc
+	sub	ip, ip, r1
+THUMB(	add	ip, ip, #1)
+	pop	{r1}
+
+	bx	ip
+
+1:
 	push	{lr}
 
 	mov	lr, r0
@@ -142,7 +161,7 @@ THUMB(	orr	lr, #1)
 	blx	lr			@ Call the HYP function
 
 	pop	{lr}
-1:	eret
+	eret
 
 guest_trap:
 	load_vcpu r0			@ Load VCPU pointer to r0
-- 
2.11.0

[PATCH 16/20] ARM: KVM: Convert __cpu_reset_hyp_mode to using __hyp_reset_vectors

[Marc Zyngier]

We are now able to use the hyp stub to reset HYP mode. Time to
kiss __kvm_hyp_reset goodbye, and use __hyp_reset_vectors.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/include/asm/kvm_asm.h  | 2 --
 arch/arm/include/asm/kvm_host.h | 3 ++-
 arch/arm/kvm/init.S             | 2 --
 3 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h
index 8ef05381984b..7ccb6f1aac5b 100644
--- a/arch/arm/include/asm/kvm_asm.h
+++ b/arch/arm/include/asm/kvm_asm.h
@@ -72,8 +72,6 @@ extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
 
 extern void __init_stage2_translation(void);
 
-extern void __kvm_hyp_reset(unsigned long);
-
 extern u64 __vgic_v3_get_ich_vtr_el2(void);
 extern void __vgic_v3_init_lrs(void);
 #endif
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index d5423ab15ed5..1962c5086897 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -277,7 +277,8 @@ static inline void __cpu_init_stage2(void)
 static inline void __cpu_reset_hyp_mode(unsigned long vector_ptr,
 					phys_addr_t phys_idmap_start)
 {
-	kvm_call_hyp((void *)virt_to_idmap(__kvm_hyp_reset), vector_ptr);
+	extern void __hyp_reset_vectors(void);
+	__hyp_reset_vectors();
 }
 
 static inline int kvm_arch_dev_ioctl_check_extension(struct kvm *kvm, long ext)
diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
index 438b148d47fd..0ec1a83d03ea 100644
--- a/arch/arm/kvm/init.S
+++ b/arch/arm/kvm/init.S
@@ -129,7 +129,6 @@ ENTRY(__kvm_handle_stub_hvc)
 
 1:	cmp	r0, #HVC_RESET_VECTORS
 	bne	1f
-ENTRY(__kvm_hyp_reset)
 	/* We're now in idmap, disable MMU */
 	mrc	p15, 4, r1, c1, c0, 0	@ HSCTLR
 	ldr	r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
@@ -153,7 +152,6 @@ ENTRY(__kvm_hyp_reset)
 exit:
 	eret
 ENDPROC(__kvm_handle_stub_hvc)
-ENDPROC(__kvm_hyp_reset)
 
 	.ltorg
 .L__va2pa:
-- 
2.11.0

[PATCH 17/20] ARM: KVM: Implement HVC_SOFT_RESTART in the init code

[Marc Zyngier]

Another missing stub hypercall is HVC_SOFT_RESTART. It turns out
that it is pretty easy to implement in terms of HVC_RESET_VECTORS
(since it needs to turn the MMU off).

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kvm/init.S | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
index 0ec1a83d03ea..489e0f79ac2c 100644
--- a/arch/arm/kvm/init.S
+++ b/arch/arm/kvm/init.S
@@ -127,8 +127,22 @@ ENTRY(__kvm_handle_stub_hvc)
 	mrc	p15, 4, r0, c12, c0, 0	@ get HVBAR
 	b	exit
 
+1:	cmp	r0, #HVC_SOFT_RESTART
+	bne	1f
+
+	/* The target is expected in r1 */
+	msr	ELR_hyp, r1
+	mrs	r0, cpsr
+	bic	r0, r0, #MODE_MASK
+	orr	r0, r0, #HYP_MODE
+THUMB(	orr	r0, r0, #PSR_T_BIT	)
+	msr	spsr_cxsf, r0
+	b	reset
+
 1:	cmp	r0, #HVC_RESET_VECTORS
 	bne	1f
+
+reset:
 	/* We're now in idmap, disable MMU */
 	mrc	p15, 4, r1, c1, c0, 0	@ HSCTLR
 	ldr	r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
-- 
2.11.0

[PATCH 18/20] arm/arm64: KVM: Simplify __cpu_reset_hyp_mode

[Marc Zyngier]

__cpu_reset_hyp_mode doesn't need to be passed any argument now,
as the hyp-stub implementations are self-contained.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/include/asm/kvm_host.h   | 3 +--
 arch/arm/kvm/arm.c                | 3 +--
 arch/arm64/include/asm/kvm_host.h | 3 +--
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 1962c5086897..370d7c6d6e7a 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -274,8 +274,7 @@ static inline void __cpu_init_stage2(void)
 	kvm_call_hyp(__init_stage2_translation);
 }
 
-static inline void __cpu_reset_hyp_mode(unsigned long vector_ptr,
-					phys_addr_t phys_idmap_start)
+static inline void __cpu_reset_hyp_mode(void)
 {
 	extern void __hyp_reset_vectors(void);
 	__hyp_reset_vectors();
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 9d7446456e0c..00b5205e8955 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -1122,8 +1122,7 @@ static void cpu_hyp_reinit(void)
 static void cpu_hyp_reset(void)
 {
 	if (!is_kernel_in_hyp_mode())
-		__cpu_reset_hyp_mode(hyp_default_vectors,
-				     kvm_get_idmap_start());
+		__cpu_reset_hyp_mode();
 }
 
 static void _kvm_arch_hardware_enable(void *discard)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 2e493e9a671e..8c8aae7cfe19 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -361,8 +361,7 @@ static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
 	__kvm_call_hyp((void *)pgd_ptr, hyp_stack_ptr, vector_ptr);
 }
 
-static inline void __cpu_reset_hyp_mode(unsigned long vector_ptr,
-					phys_addr_t phys_idmap_start)
+static inline void __cpu_reset_hyp_mode(void)
 {
 	extern void __hyp_reset_vectors(void);
 	__hyp_reset_vectors();
-- 
2.11.0

[PATCH 19/20] arm/arm64: KVM: Remove kvm_get_idmap_start

[Marc Zyngier]

With __cpu_reset_hyp_mode having become fairly dumb, there is no
need for kvm_get_idmap_start anymore.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/include/asm/kvm_mmu.h   | 1 -
 arch/arm/kvm/mmu.c               | 5 -----
 arch/arm64/include/asm/kvm_mmu.h | 1 -
 3 files changed, 7 deletions(-)

diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index 74a44727f8e1..646a4d4236ba 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -56,7 +56,6 @@ void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu);
 
 phys_addr_t kvm_mmu_get_httbr(void);
 phys_addr_t kvm_get_idmap_vector(void);
-phys_addr_t kvm_get_idmap_start(void);
 int kvm_mmu_init(void);
 void kvm_clear_hyp_idmap(void);
 
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index a5265edbeeab..12ab3372f240 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1677,11 +1677,6 @@ phys_addr_t kvm_get_idmap_vector(void)
 	return hyp_idmap_vector;
 }
 
-phys_addr_t kvm_get_idmap_start(void)
-{
-	return hyp_idmap_start;
-}
-
 static int kvm_map_idmap_text(pgd_t *pgd)
 {
 	int err;
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 6f72fe8b0e3e..ff1282344ece 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -155,7 +155,6 @@ void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu);
 
 phys_addr_t kvm_mmu_get_httbr(void);
 phys_addr_t kvm_get_idmap_vector(void);
-phys_addr_t kvm_get_idmap_start(void);
 int kvm_mmu_init(void);
 void kvm_clear_hyp_idmap(void);
 
-- 
2.11.0

[PATCH 20/20] arm/arm64: Add hyp-stub API documentation

[Marc Zyngier]

In order to help people understanding the hyp-stub API that exists
between the host kernel and the hypervisor mode (whether a hypervisor
has been installed or not), let's document said API.

As as with any form of documentation, I expect it to become obsolete
and completely misleading within 20 minutes after having being merged.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 Documentation/virtual/kvm/arm/hyp-abi.txt | 48 +++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 Documentation/virtual/kvm/arm/hyp-abi.txt

diff --git a/Documentation/virtual/kvm/arm/hyp-abi.txt b/Documentation/virtual/kvm/arm/hyp-abi.txt
new file mode 100644
index 000000000000..ad3e16fe723c
--- /dev/null
+++ b/Documentation/virtual/kvm/arm/hyp-abi.txt
@@ -0,0 +1,48 @@
+* Internal ABI between the kernel and HYP
+
+This file documents the interaction between the Linux kernel and the
+hypervisor layer when running Linux as a hypervisor (for example
+KVM). It doesn't cover the interaction of the kernel with the
+hypervisor when running as a guest (under Xen, KVM or any other
+hypervisor), or any hypervisor-specific interaction when the kernel is
+used as a host.
+
+On arm and arm64 (without VHE), the kernel doesn't run in hypervisor
+mode, but still needs to interact with it, allowing a built-in
+hypervisor to be either installed or torn down.
+
+In order to achieve this, the kernel must be booted at HYP (arm) or
+EL2 (arm64), allowing it to install a set of stubs before dropping to
+SVC/EL1. These stubs are accessible by using a 'hvc #0' instruction,
+and only act on individual CPUs.
+
+Unless specified otherwise, any built-in hypervisor must implement
+these functions (see arch/arm{,64}/include/asm/virt.h):
+
+* r0/x0 = HVC_GET_VECTORS
+
+  Return the current value of HVBAR/VBAR_EL2 in r0/x0.
+
+* r0/x0 = HVC_SET_VECTORS
+  r1/x1 = vectors
+
+  Set HVBAR/VBAR_EL2 to 'vectors' to enable a hypervisor. Only
+  implemented by the initial stubs.
+
+* r0/x0 = HVC_RESET_VECTORS
+
+  Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the default
+  value. This effectively disables an existing hypervisor.
+
+* r0/x0 = HVC_SOFT_RESTART
+  r1/x1 = restart address
+  x2 = x0's value when entering the next payload (arm64)
+  x3 = x1's value when entering the next payload (arm64)
+  x4 = x2's value when entering the next payload (arm64)
+
+  Mask all exceptions, disable the MMU, move the arguments into place
+  (arm64 only), and jump to the restart address while at HYP/EL2. This
+  hypercall is not expected to return to its caller.
+
+Any other value of r0/x0 triggers a hypervisor-specific handling,
+which is not documented here.
-- 
2.11.0