Subject: Re: [PATCH v3 02/12] KVM: arm64: selftests: Add write_sysreg_s and read_sysreg_s

From: Oliver Upton <[email-masked]>
Date: Wed, 1 Sep 2021 21:28:28 +0000

On Wed, Sep 01, 2021 at 09:14:02PM +0000, Raghavendra Rao Ananta wrote:
> For register names that are unsupported by the assembler or the ones
> without architectural names, add the macros write_sysreg_s and
> read_sysreg_s to support them.
> 
> The functionality is derived from kvm-unit-tests and kernel's
> arch/arm64/include/asm/sysreg.h.
> 
> Signed-off-by: Raghavendra Rao Ananta <[email-masked]>

Would it be possible to just include <asm/sysreg.h>? See
tools/arch/arm64/include/asm/sysreg.h

> ---
>  .../selftests/kvm/include/aarch64/processor.h | 61 +++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/aarch64/processor.h b/tools/testing/selftests/kvm/include/aarch64/processor.h
> index 3cbaf5c1e26b..082cc97ad8d3 100644
> --- a/tools/testing/selftests/kvm/include/aarch64/processor.h
> +++ b/tools/testing/selftests/kvm/include/aarch64/processor.h
> @@ -118,6 +118,67 @@ void vm_install_exception_handler(struct kvm_vm *vm,
>  void vm_install_sync_handler(struct kvm_vm *vm,
>  		int vector, int ec, handler_fn handler);
>  
> +/*
> + * ARMv8 ARM reserves the following encoding for system registers:
> + * (Ref: ARMv8 ARM, Section: "System instruction class encoding overview",
> + *  C5.2, version:ARM DDI 0487A.f)
> + *	[20-19] : Op0
> + *	[18-16] : Op1
> + *	[15-12] : CRn
> + *	[11-8]  : CRm
> + *	[7-5]   : Op2
> + */
> +#define Op0_shift	19
> +#define Op0_mask	0x3
> +#define Op1_shift	16
> +#define Op1_mask	0x7
> +#define CRn_shift	12
> +#define CRn_mask	0xf
> +#define CRm_shift	8
> +#define CRm_mask	0xf
> +#define Op2_shift	5
> +#define Op2_mask	0x7
> +
> +/*
> + * When accessed from guests, the ARM64_SYS_REG() doesn't work since it
> + * generates a different encoding for additional KVM processing, and is
> + * only suitable for userspace to access the register via ioctls.
> + * Hence, define a 'pure' sys_reg() here to generate the encodings as per spec.
> + */
> +#define sys_reg(op0, op1, crn, crm, op2) \
> +	(((op0) << Op0_shift) | ((op1) << Op1_shift) | \
> +	 ((crn) << CRn_shift) | ((crm) << CRm_shift) | \
> +	 ((op2) << Op2_shift))
> +
> +asm(
> +"	.irp	num,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30\n"
> +"	.equ	.L__reg_num_x\\num, \\num\n"
> +"	.endr\n"
> +"	.equ	.L__reg_num_xzr, 31\n"
> +"\n"
> +"	.macro	mrs_s, rt, sreg\n"
> +"	.inst	0xd5200000|(\\sreg)|(.L__reg_num_\\rt)\n"
> +"	.endm\n"
> +"\n"
> +"	.macro	msr_s, sreg, rt\n"
> +"	.inst	0xd5000000|(\\sreg)|(.L__reg_num_\\rt)\n"
> +"	.endm\n"
> +);
> +
> +/*
> + * read_sysreg_s() and write_sysreg_s()'s 'reg' has to be encoded via sys_reg()
> + */
> +#define read_sysreg_s(reg) ({						\
> +	u64 __val;							\
> +	asm volatile("mrs_s %0, "__stringify(reg) : "=r" (__val));	\
> +	__val;								\
> +})
> +
> +#define write_sysreg_s(reg, val) do {					\
> +	u64 __val = (u64)val;						\
> +	asm volatile("msr_s "__stringify(reg) ", %x0" : : "rZ" (__val));\
> +} while (0)
> +
>  #define write_sysreg(reg, val)						  \
>  ({									  \
>  	u64 __val = (u64)(val);						  \
> -- 
> 2.33.0.153.gba50c8fa24-goog
> 

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