linux-kernel - Re: [patch 15/31] x86/fpu: Rework copy_xstate_to_uabi

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Date:   Tue, 12 Oct 2021 19:30:58 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Chang S. Bae" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        kvm@...r.kernel.org
Subject: Re: [patch 15/31] x86/fpu: Rework copy_xstate_to_uabi_buf()

On 12/10/21 02:00, Thomas Gleixner wrote:
> Prepare for replacing the KVM copy xstate to user function by extending
> copy_xstate_to_uabi_buf() with a pkru argument which allows the caller to
> hand in the pkru value, which is required for KVM because the guest PKRU is
> not accessible via current. Fixup all callsites accordingly.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>   arch/x86/kernel/fpu/xstate.c |   34 ++++++++++++++++++++++++++--------
>   arch/x86/kernel/fpu/xstate.h |    3 +++
>   2 files changed, 29 insertions(+), 8 deletions(-)
> 
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -940,9 +940,10 @@ static void copy_feature(bool from_xstat
>   }
>   
>   /**
> - * copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer
> + * __copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer
>    * @to:		membuf descriptor
> - * @tsk:	The task from which to copy the saved xstate
> + * @xsave:	The xsave from which to copy
> + * @pkru_val:	The PKRU value to store in the PKRU component
>    * @copy_mode:	The requested copy mode
>    *
>    * Converts from kernel XSAVE or XSAVES compacted format to UABI conforming
> @@ -951,11 +952,10 @@ static void copy_feature(bool from_xstat
>    *
>    * It supports partial copy but @to.pos always starts from zero.
>    */
> -void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
> -			     enum xstate_copy_mode copy_mode)
> +void __copy_xstate_to_uabi_buf(struct membuf to, struct xregs_state *xsave,
> +			       u32 pkru_val, enum xstate_copy_mode copy_mode)
>   {
>   	const unsigned int off_mxcsr = offsetof(struct fxregs_state, mxcsr);
> -	struct xregs_state *xsave = &tsk->thread.fpu.state.xsave;
>   	struct xregs_state *xinit = &init_fpstate.xsave;
>   	struct xstate_header header;
>   	unsigned int zerofrom;
> @@ -1033,10 +1033,9 @@ void copy_xstate_to_uabi_buf(struct memb
>   			struct pkru_state pkru = {0};
>   			/*
>   			 * PKRU is not necessarily up to date in the
> -			 * thread's XSAVE buffer.  Fill this part from the
> -			 * per-thread storage.
> +			 * XSAVE buffer. Use the provided value.
>   			 */
> -			pkru.pkru = tsk->thread.pkru;
> +			pkru.pkru = pkru_val;
>   			membuf_write(&to, &pkru, sizeof(pkru));
>   		} else {
>   			copy_feature(header.xfeatures & BIT_ULL(i), &to,
> @@ -1056,6 +1055,25 @@ void copy_xstate_to_uabi_buf(struct memb
>   		membuf_zero(&to, to.left);
>   }
>   
> +/**
> + * copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer
> + * @to:		membuf descriptor
> + * @tsk:	The task from which to copy the saved xstate
> + * @copy_mode:	The requested copy mode
> + *
> + * Converts from kernel XSAVE or XSAVES compacted format to UABI conforming
> + * format, i.e. from the kernel internal hardware dependent storage format
> + * to the requested @mode. UABI XSTATE is always uncompacted!
> + *
> + * It supports partial copy but @to.pos always starts from zero.
> + */
> +void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
> +			     enum xstate_copy_mode copy_mode)
> +{
> +	__copy_xstate_to_uabi_buf(to, &tsk->thread.fpu.state.xsave,
> +				  tsk->thread.pkru, copy_mode);
> +}
> +
>   static int copy_from_buffer(void *dst, unsigned int offset, unsigned int size,
>   			    const void *kbuf, const void __user *ubuf)
>   {
> --- a/arch/x86/kernel/fpu/xstate.h
> +++ b/arch/x86/kernel/fpu/xstate.h
> @@ -15,4 +15,7 @@ static inline void xstate_init_xcomp_bv(
>   		xsave->header.xcomp_bv = mask | XCOMP_BV_COMPACTED_FORMAT;
>   }
>   
> +extern void __copy_xstate_to_uabi_buf(struct membuf to, struct xregs_state *xsave,
> +				      u32 pkru_val, enum xstate_copy_mode copy_mode);
> +
>   #endif
> 

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>