linux-kernel - Re: [PATCH v4 09/15] KVM: SEV: sync FPU and AVX state at LAUNCH_UPDATE

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Date: Tue, 19 Mar 2024 08:42:19 -0500
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<isaku.yamahata@...el.com>, <seanjc@...gle.com>, Dave Hansen
	<dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 09/15] KVM: SEV: sync FPU and AVX state at
 LAUNCH_UPDATE_VMSA time

On Mon, Mar 18, 2024 at 07:33:46PM -0400, Paolo Bonzini wrote:
> SEV-ES allows passing custom contents for x87, SSE and AVX state into the VMSA.
> Allow userspace to do that with the usual KVM_SET_XSAVE API and only mark
> FPU contents as confidential after it has been copied and encrypted into
> the VMSA.
> 
> Since the XSAVE state for AVX is the first, it does not need the
> compacted-state handling of get_xsave_addr().  However, there are other
> parts of XSAVE state in the VMSA that currently are not handled, and
> the validation logic of get_xsave_addr() is pointless to duplicate
> in KVM, so move get_xsave_addr() to public FPU API; it is really just
> a facility to operate on XSAVE state and does not expose any internal
> details of arch/x86/kernel/fpu.
> 
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/include/asm/fpu/api.h |  3 +++
>  arch/x86/kernel/fpu/xstate.h   |  2 --
>  arch/x86/kvm/svm/sev.c         | 36 ++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/svm/svm.c         |  8 --------
>  4 files changed, 39 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
> index a2be3aefff9f..f86ad3335529 100644
> --- a/arch/x86/include/asm/fpu/api.h
> +++ b/arch/x86/include/asm/fpu/api.h
> @@ -143,6 +143,9 @@ extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfe
>  
>  extern u64 xstate_get_guest_group_perm(void);
>  
> +extern void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);

I get a linker error if I don't add an EXPORT_SYMBOL_GPL(get_xsave_addr)

-Mike