Re: [PATCH 1/2] ARM: hyp-stub: improve ABI

Marc Zyngier
2016-12-15T11:17:45Z

On 14/12/16 10:46, Russell King wrote:
> 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

This breaks the KVM implementation of __hyp_get_vectors, easily fixed
with the following patchlet:

diff --git a/arch/arm/include/asm/virt.h b/arch/arm/include/asm/virt.h
index a2e75b8..0fe637e 100644
--- a/arch/arm/include/asm/virt.h
+++ b/arch/arm/include/asm/virt.h
@@ -89,6 +89,14 @@ 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 ebc26f8..1c6888f 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 96beb53..1f8db7d 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

Thanks,

M.
--
Jazz is not dead. It just smells funny...