Subject: Re: [PATCH 04/18] KVM: arm64: pkvm: Remove struct cpu_sve_state

From: Vladimir Murzin <[email-masked]>
Date: Wed, 27 May 2026 12:58:47 +0100

Hi Mark,

On 5/21/26 14:25, Mark Rutland wrote:
> There's no need for struct cpu_sve_state. Code would be simpler and more
> robust without it, and removing it will simplify further cleanups (e.g.
> adding an opaque type for the sve register state).
> 
> Protected KVM stores most of the host's system register state in
> kvm_host_data::host_ctxt, which is an instance of struct
> kvm_cpu_context. As kvm_cpu_context::sys_regs[] has a slot for ZCR_EL1,
> we can store the host's ZCR_EL1 there.
> 
> While kvm_cpu_context::sys_regs doesn't have slots for FPSR and FPCR,
> these are usually expected to be stored in struct user_fpsimd_state.
> For historical reasons, __sve_save_state and __sve_restore_state()
> expect a pointer to fpsr *within* struct user_fpsimd_state, assuming the
> fpcr will immediately follow, as per the order within struct
> user_fpsimd_state. We currently match this ordering in struct
> cpu_sve_state, but it would be simpler and more robust to use struct
> user_fpsimd_state directly.
> 
> After moving ZCR_EL1, FPSR, and FPCR out of struct cpu_sve_state, all
> that's left is sve_regs, which can be represented as a pointer without
> need for a container struct. This is kept as a pointer to u8 (matching
> the array type), as this permits the compiler to catch unbalanced
> referencing/dereferencing, which is not possible for pointers to void.
> 
> Apply the above changes, and remove cpu_sve_state.
> 
> Signed-off-by: Mark Rutland <[email-masked]>
> Cc: Catalin Marinas <[email-masked]>
> Cc: Fuad Tabba <[email-masked]>
> Cc: James Morse <[email-masked]>
> Cc: Marc Zyngier <[email-masked]>
> Cc: Mark Brown <[email-masked]>
> Cc: Oliver Upton <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> ---
>  arch/arm64/include/asm/kvm_host.h       | 18 ++----------------
>  arch/arm64/include/asm/kvm_pkvm.h       |  3 +--
>  arch/arm64/kvm/arm.c                    | 16 ++++++++--------
>  arch/arm64/kvm/hyp/include/hyp/switch.h |  9 +++++----
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c      |  9 +++++----
>  arch/arm64/kvm/hyp/nvhe/setup.c         |  4 ++--
>  6 files changed, 23 insertions(+), 36 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 42b1c4764a4bf..ae24617380b8f 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -732,20 +732,6 @@ struct kvm_cpu_context {
>  	u64 *vncr_array;
>  };
>  
> -struct cpu_sve_state {
> -	__u64 zcr_el1;
> -
> -	/*
> -	 * Ordering is important since __sve_save_state/__sve_restore_state
> -	 * relies on it.
> -	 */
> -	__u32 fpsr;
> -	__u32 fpcr;
> -
> -	/* Must be SVE_VQ_BYTES (128 bit) aligned. */
> -	__u8 sve_regs[];

It seems that the requirement (driven by SVE ldr/str) is
satisfied with the new sve_regs pointing to the start of the
page.

I'm not sure whether we want to keep the comment (or perhaps
enforce this with explicit checks) so that future refactoring
doesn't lead to time spent debugging alignment faults...

> -};
> -
>  /*
>   * This structure is instantiated on a per-CPU basis, and contains
>   * data that is:
> @@ -771,9 +757,9 @@ struct kvm_host_data {
>  
>  	/*
>  	 * Hyp VA.
> -	 * sve_state is only used in pKVM and if system_supports_sve().
> +	 * sve_regs is only used in pKVM and if system_supports_sve().
>  	 */
> -	struct cpu_sve_state *sve_state;
> +	u8	*sve_regs;
>  
>  	/* Ownership of the FP regs */
>  	enum {
> diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
> index 2954b311128c7..74fedd9c5ff02 100644
> --- a/arch/arm64/include/asm/kvm_pkvm.h
> +++ b/arch/arm64/include/asm/kvm_pkvm.h
> @@ -188,8 +188,7 @@ static inline size_t pkvm_host_sve_state_size(void)
>  	if (!system_supports_sve())
>  		return 0;
>  
> -	return size_add(sizeof(struct cpu_sve_state),
> -			SVE_SIG_REGS_SIZE(sve_vq_from_vl(kvm_host_sve_max_vl)));
> +	return SVE_SIG_REGS_SIZE(sve_vq_from_vl(kvm_host_sve_max_vl));
>  }
>  
>  struct pkvm_mapping {
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 8bb2c7422cc8b..f9fc85a0344e1 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2499,10 +2499,10 @@ static void __init teardown_hyp_mode(void)
>  			continue;
>  
>  		if (free_sve) {
> -			struct cpu_sve_state *sve_state;
> +			u8 *sve_regs;
>  
> -			sve_state = per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_state;
> -			free_pages((unsigned long) sve_state, pkvm_host_sve_state_order());
> +			sve_regs = per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_regs;
> +			free_pages((unsigned long) sve_regs, pkvm_host_sve_state_order());
>  		}
>  
>  		free_pages(kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu], nvhe_percpu_order());
> @@ -2627,7 +2627,7 @@ static int init_pkvm_host_sve_state(void)
>  		if (!page)
>  			return -ENOMEM;
>  
> -		per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_state = page_address(page);
> +		per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_regs = page_address(page);
>  	}
>  
>  	/*
> @@ -2648,11 +2648,11 @@ static void finalize_init_hyp_mode(void)
>  
>  	if (system_supports_sve() && is_protected_kvm_enabled()) {
>  		for_each_possible_cpu(cpu) {
> -			struct cpu_sve_state *sve_state;
> +			u8 *sve_regs;
>  
> -			sve_state = per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_state;
> -			per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_state =
> -				kern_hyp_va(sve_state);
> +			sve_regs = per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_regs;
> +			per_cpu_ptr_nvhe_sym(kvm_host_data, cpu)->sve_regs =
> +				kern_hyp_va(sve_regs);
>  		}
>  	}
>  }
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index cc4d011a2b380..6512dd3f75ae4 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -484,12 +484,13 @@ static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu)
>  
>  static inline void __hyp_sve_save_host(void)
>  {
> -	struct cpu_sve_state *sve_state = *host_data_ptr(sve_state);
> +	struct kvm_cpu_context *hctxt = host_data_ptr(host_ctxt);
> +	u8 *sve_regs = *host_data_ptr(sve_regs);
>  
> -	sve_state->zcr_el1 = read_sysreg_el1(SYS_ZCR);
> +	ctxt_sys_reg(hctxt, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
>  	write_sysreg_s(sve_vq_from_vl(kvm_host_sve_max_vl) - 1, SYS_ZCR_EL2);
> -	__sve_save_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
> -			 &sve_state->fpsr,
> +	__sve_save_state(sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
> +			 &hctxt->fp_regs.fpsr,
>  			 true);
>  }
>  
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index db60f770060e5..04a6d2e0ea73f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -41,7 +41,8 @@ static void __hyp_sve_save_guest(struct kvm_vcpu *vcpu)
>  
>  static void __hyp_sve_restore_host(void)
>  {
> -	struct cpu_sve_state *sve_state = *host_data_ptr(sve_state);
> +	struct kvm_cpu_context *hctxt = host_data_ptr(host_ctxt);
> +	u8 *sve_regs = *host_data_ptr(sve_regs);
>  
>  	/*
>  	 * On saving/restoring host sve state, always use the maximum VL for
> @@ -53,10 +54,10 @@ static void __hyp_sve_restore_host(void)
>  	 * need to be revisited.
>  	 */
>  	write_sysreg_s(sve_vq_from_vl(kvm_host_sve_max_vl) - 1, SYS_ZCR_EL2);
> -	__sve_restore_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
> -			    &sve_state->fpsr,
> +	__sve_restore_state(sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
> +			    &hctxt->fp_regs.fpsr,
>  			    true);
> -	write_sysreg_el1(sve_state->zcr_el1, SYS_ZCR);
> +	write_sysreg_el1(ctxt_sys_reg(hctxt, ZCR_EL1), SYS_ZCR);
>  }
>  
>  static void fpsimd_sve_flush(void)
> diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
> index d461981616d90..cdaf53c833409 100644
> --- a/arch/arm64/kvm/hyp/nvhe/setup.c
> +++ b/arch/arm64/kvm/hyp/nvhe/setup.c
> @@ -82,9 +82,9 @@ static int pkvm_create_host_sve_mappings(void)
>  
>  	for (i = 0; i < hyp_nr_cpus; i++) {
>  		struct kvm_host_data *host_data = per_cpu_ptr(&kvm_host_data, i);
> -		struct cpu_sve_state *sve_state = host_data->sve_state;
> +		u8 *sve_regs = host_data->sve_regs;
>  
> -		start = kern_hyp_va(sve_state);
> +		start = kern_hyp_va(sve_regs);
>  		end = start + PAGE_ALIGN(pkvm_host_sve_state_size());
>  		ret = pkvm_create_mappings(start, end, PAGE_HYP);
>  		if (ret)
> -- 2.30.2
> 

FWIW,

Reviewed-by: Vladimir Murzin <[email-masked]>