linux-kernel - Re: [PATCH v8 05/21] x86/cea: Export API for per-CPU exception stacks for KVM

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Message-ID: <20251023080627.GV3245006@noisy.programming.kicks-ass.net>
Date: Thu, 23 Oct 2025 10:06:27 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Xin Li (Intel)" <xin@...or.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-doc@...r.kernel.org, pbonzini@...hat.com, seanjc@...gle.com,
	corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	luto@...nel.org, andrew.cooper3@...rix.com, chao.gao@...el.com,
	hch@...radead.org
Subject: Re: [PATCH v8 05/21] x86/cea: Export API for per-CPU exception
 stacks for KVM

On Mon, Oct 13, 2025 at 06:09:34PM -0700, Xin Li (Intel) wrote:

> FRED introduced new fields in the host-state area of the VMCS for stack
> levels 1->3 (HOST_IA32_FRED_RSP[123]), each respectively corresponding to
> per-CPU exception stacks for #DB, NMI and #DF.  KVM must populate these
> fields each time a vCPU is loaded onto a CPU.

> +noinstr unsigned long __this_cpu_ist_top_va(enum exception_stack_ordering stack)
> +{
> +	return __this_cpu_ist_bottom_va(stack) + EXCEPTION_STKSZ;
> +}
> +EXPORT_SYMBOL(__this_cpu_ist_top_va);

This has no business being a !GPL export. But please use:

EXPORT_SYMBOL_FOR_MODULES(__this_cpu_ist_top_val, "kvm");

(or "kvm-intel", depending on which actual module ends up needing this
symbol).