linux-kernel - Re: [PATCH v7 05/26] x86/fpu/xstate: Introduce fpu_guest

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Date:   Thu, 30 Nov 2023 19:29:28 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com,
        pbonzini@...hat.com, dave.hansen@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, chao.gao@...el.com,
        rick.p.edgecombe@...el.com, john.allen@....com
Subject: Re: [PATCH v7 05/26] x86/fpu/xstate: Introduce fpu_guest_cfg for
 guest FPU configuration

On Fri, 2023-11-24 at 00:53 -0500, Yang Weijiang wrote:
> Define new fpu_guest_cfg to hold all guest FPU settings so that it can
> differ from generic kernel FPU settings, e.g., enabling CET supervisor
> xstate by default for guest fpstate while it's remained disabled in
> kernel FPU config.
> 
> The kernel dynamic xfeatures are specifically used by guest fpstate now,
> add the mask for guest fpstate so that guest_perm.__state_permit ==
> (fpu_kernel_cfg.default_xfeature | XFEATURE_MASK_KERNEL_DYNAMIC). And
> if guest fpstate is re-allocated to hold user dynamic xfeatures, the
> resulting permissions are consumed before calculate new guest fpstate.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/include/asm/fpu/types.h |  2 +-
>  arch/x86/kernel/fpu/core.c       | 14 +++++++++++---
>  arch/x86/kernel/fpu/xstate.c     | 10 ++++++++++
>  3 files changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> index c6fd13a17205..306825ad6bc0 100644
> --- a/arch/x86/include/asm/fpu/types.h
> +++ b/arch/x86/include/asm/fpu/types.h
> @@ -602,6 +602,6 @@ struct fpu_state_config {
>  };
>  
>  /* FPU state configuration information */
> -extern struct fpu_state_config fpu_kernel_cfg, fpu_user_cfg;
> +extern struct fpu_state_config fpu_kernel_cfg, fpu_user_cfg, fpu_guest_cfg;
>  
>  #endif /* _ASM_X86_FPU_H */
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index a21a4d0ecc34..516af626bf6a 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -33,9 +33,10 @@ DEFINE_STATIC_KEY_FALSE(__fpu_state_size_dynamic);
>  DEFINE_PER_CPU(u64, xfd_state);
>  #endif
>  
> -/* The FPU state configuration data for kernel and user space */
> +/* The FPU state configuration data for kernel, user space and guest. */
>  struct fpu_state_config	fpu_kernel_cfg __ro_after_init;
>  struct fpu_state_config fpu_user_cfg __ro_after_init;
> +struct fpu_state_config fpu_guest_cfg __ro_after_init;
>  
>  /*
>   * Represents the initial FPU state. It's mostly (but not completely) zeroes,
> @@ -536,8 +537,15 @@ void fpstate_reset(struct fpu *fpu)
>  	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;
>  	fpu->perm.__state_size		= fpu_kernel_cfg.default_size;
>  	fpu->perm.__user_state_size	= fpu_user_cfg.default_size;
> -	/* Same defaults for guests */
> -	fpu->guest_perm = fpu->perm;
> +
> +	/* Guest permission settings */
> +	fpu->guest_perm.__state_perm	= fpu_guest_cfg.default_features;
> +	fpu->guest_perm.__state_size	= fpu_guest_cfg.default_size;
> +	/*
> +	 * Set guest's __user_state_size to fpu_user_cfg.default_size so that
> +	 * existing uAPIs can still work.
> +	 */
> +	fpu->guest_perm.__user_state_size = fpu_user_cfg.default_size;
>  }
>  
>  static inline void fpu_inherit_perms(struct fpu *dst_fpu)
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index ba4172172afd..aa8f8595cd41 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -681,6 +681,7 @@ static int __init init_xstate_size(void)
>  {
>  	/* Recompute the context size for enabled features: */
>  	unsigned int user_size, kernel_size, kernel_default_size;
> +	unsigned int guest_default_size;
>  	bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
>  
>  	/* Uncompacted user space size */
> @@ -702,13 +703,18 @@ static int __init init_xstate_size(void)
>  	kernel_default_size =
>  		xstate_calculate_size(fpu_kernel_cfg.default_features, compacted);
>  
> +	guest_default_size =
> +		xstate_calculate_size(fpu_guest_cfg.default_features, compacted);
> +
>  	if (!paranoid_xstate_size_valid(kernel_size))
>  		return -EINVAL;
>  
>  	fpu_kernel_cfg.max_size = kernel_size;
>  	fpu_user_cfg.max_size = user_size;
> +	fpu_guest_cfg.max_size = kernel_size;
>  
>  	fpu_kernel_cfg.default_size = kernel_default_size;
> +	fpu_guest_cfg.default_size = guest_default_size;
>  	fpu_user_cfg.default_size =
>  		xstate_calculate_size(fpu_user_cfg.default_features, false);
>  
> @@ -829,6 +835,10 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
>  	fpu_user_cfg.default_features = fpu_user_cfg.max_features;
>  	fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
>  
> +	fpu_guest_cfg.max_features = fpu_kernel_cfg.max_features;
> +	fpu_guest_cfg.default_features = fpu_guest_cfg.max_features;
> +	fpu_guest_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
> +
>  	/* Store it for paranoia check at the end */
>  	xfeatures = fpu_kernel_cfg.max_features;
>  

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky