Subject: Re: [PATCH v8 5/6] KVM: arm64: Reuse fields of sys_reg_desc for idreg

From: Cornelia Huck <[email-masked]>
Date: Tue, 16 May 2023 12:26:11 +0200

On Wed, May 03 2023, Jing Zhang <[email-masked]> wrote:

> Since reset() and val are not used for idreg in sys_reg_desc, they would
> be used with other purposes for idregs.
> The callback reset() would be used to return KVM sanitised id register
> values. The u64 val would be used as mask for writable fields in idregs.
> Only bits with 1 in val are writable from userspace.
>
> Signed-off-by: Jing Zhang <[email-masked]>
> ---
>  arch/arm64/kvm/id_regs.c  | 44 +++++++++++++++++++----------
>  arch/arm64/kvm/sys_regs.c | 59 +++++++++++++++++++++++++++------------
>  arch/arm64/kvm/sys_regs.h | 10 ++++---
>  3 files changed, 77 insertions(+), 36 deletions(-)
>

(...)

> diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
> index e88fd77309b2..21869319f6e1 100644
> --- a/arch/arm64/kvm/sys_regs.h
> +++ b/arch/arm64/kvm/sys_regs.h
> @@ -65,12 +65,12 @@ struct sys_reg_desc {
>  		       const struct sys_reg_desc *);
>  
>  	/* Initialization for vcpu. */

Maybe be a bit more verbose here?

/* Initialization for vcpu. Return initialized value, or KVM sanitized
   value for id registers. */

> -	void (*reset)(struct kvm_vcpu *, const struct sys_reg_desc *);
> +	u64 (*reset)(struct kvm_vcpu *, const struct sys_reg_desc *);
>  
>  	/* Index into sys_reg[], or 0 if we don't need to save it. */
>  	int reg;
>  
> -	/* Value (usually reset value) */
> +	/* Value (usually reset value), or write mask for idregs */
>  	u64 val;
>  
>  	/* Custom get/set_user functions, fallback to generic if NULL */

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